Gideon Algernon Mantell

FOSSIL ZOOPHYTES.—PORIFERA OR AMORPHOZOA—POLYPIFERA OR CORALS—BRYOZOA OR MOLLUSCAN ZOOPHYTES.

Many tribes of the extraordinary beings whose mineralized relics are the immediate subject of our investigation, have largely contributed to the solid materials of which the sedimentary strata are composed. In the most ancient rocks in which vestiges of organic structures have been detected, those of Zoophytes hold a conspicuous place; and in the seas of tropical climates, the agency of the Coral-animalcules, or Polypifera, is producing enormous deposits, and laying the foundations of new islands and continents, and forming reefs of rocks hundreds of miles in extent, which, if elevated above the level of the sea, would rival in magnitude the mountain-chains of modern Europe.

The reader unacquainted with the natural history of these marvellous creatures will find an account of their nature and economy, and of the physical effects produced on the earth's surface by their agency, in the sixth lecture of Wond. vol. ii. p. 588.

The term Zoophytes, or animal-plants, comprises two very distinct classes of living beings, namely, the Porifera, or Sponges, which (if not vegetables) are wanting in many attributes regarded as essential characteristics of the members of the animal kingdom; and the Polypifera, or polype-bearing-animals,—the Corals; which are generally associated groups or aggregations of individuals, united by a common organized mass or axis, each polype having an independent existence, and exhibiting volition and perception, in a greater or lesser degree.

Fossil Porifera.

FOSSIL PORIFERA.

The terms Amorphozoa (signifying animals of variable shapes), and Porifera (structures traversed by pores or channels), are employed by naturalists to designate the Sponges and analogous organisms, which appear to occupy the boundary line that separates the animal from the vegetable kingdom. The true position of the Sponges in the great system of Creation is still a disputed point; for while many distinguished naturalists regard them as Protozoa, or the lowest type of animal organization, others of equal eminence affirm that neither in structure nor functions do they differ from vegetables in any essential particular; and that if a line be drawn between the two kingdoms the Porifera must be placed on the vegetable side of the boundary. On the other hand, Dr. George Johnston, in his delightful work on the British Zoophytes,[193] expresses his opinion that there is nothing to discountenance the belief that these bodies hold an intermediate place; that they are, in fact, the true Zoophytes, or animal-plants; in some forms, as the green SpongillÆ of our lakes, the vegetable nature prevails; while in others, as the horny or keratose sponges filled with mucilaginous slime, and the fleshy Tethya whose oscula, or pores, are said to exhibit signs of irritability, the animal character predominates.

[193] A History of British Sponges, &c. by Dr. George Johnston, Edinburgh. 1843. One vol. 8vo. with twenty-five plates. A previous work, "A History of British Zoophytes," with forty-four plates, from drawings by the accomplished lady of the Author, cannot be too highly commended.

Without committing ourselves to either opinion, and simply remarking that the large proportion of silex that enters into the tissues of a considerable number of the porifera, is more characteristic of vegetable than of animal structures, we proceed to consider the fossil sponges and allied forms, as the mineralized remains of the lowest types of the animal kingdom: if the vegetable nature of the originals were generally admitted, this section should have followed that which treats of the DiatomaceÆ (ante, p. 100.).

Sponge consists of a reticulated fibrous mass, covered with numerous pores of various sizes, which are connected internally by anastomosing channels, and this tissue is surrounded by a cellular gelatinous matter, by which the entire structure was secreted, and is, in fact, the vital part of the zoophyte. The tough framework or skeleton is in some kinds fibrous, horny, flexible, or rigid, and strengthened by calcareous or siliceous spicula (spines);[194] while in other species its substance is calcareous, and in some siliceous, constituting a web of transparent rock crystal, resembling spun glass,[195] The gelatinous matter lines all the cavities, and forms the margins of the openings; it presents no signs of irritability, and may be easily pressed out of the porous mass with the hand, so slight is the connexion between the skeleton and the investing tissue. Currents of water constantly enter the small pores, traverse the inosculating canals, and issue from the larger orifices, which often project above the surface in perforated papillÆ. By the circulation of the water through the porous structure, the nutrition of the organized mass is effected; and the modifications observable in the number, size, form, and disposition of the pores, channels, and orifices, in different species, appear to be subservient to this especial purpose; the imbibition and expulsion of water being the only function the sponges perform. In its earliest stage the sponge gemmule is of a spheroidal shape, and covered with vibratile cilia, and after expulsion from the canals in which it is formed, moves rapidly through the water till it becomes attached to some body, and is then immovably fixed during life; exhibiting no signs of vitality save the aqueous circulation through the pores and canals.

[194] The Mediterranean and American sponges of commerce are devoid of spicules, and are deprived of their soft animal matter simply by washing freely in fresh water.[195] I particularly allude to a siliceous Sponge from Barbadoes, named, by Mr. Samuel Stutchbury, formerly of the Bristol Institution, (now of Australia.) Dictyochalix pumicea. This specimen is of a fungiform shape, and appears to the naked eye as if formed of pumice stone, but under the microscope is literally a tissue of transparent silex.

There is much confusion in the arrangement and nomenclature of the fossil species of this class of zoophytes; and this has originated, in part, from the varied forms assumed by the same species, having been described under different names; and from the reprehensible practice of changing, without sufficient reason, the name assigned to a species by the original discoverer; an evil, unfortunately, not restricted to this department of natural history.

The recent Sponges are arranged in four groups according to their structure, viz.—

Fresh-water Sponges.

Spongilla: siliceous spicula in a translucent jelly-like mass.

Marine Sponges.

Tethea: having a tough outer skin; siliceous spicula in bundles, and radiating from the compact nucleus to the periphery.

Halichondria: (from silex and cartilago) siliceous spicula in a cartilaginous mass.

Grantia: calcareous spicula in a gelatinous mass.

FOSSIL SPONGES.

M. D'Orbigny seems to believe that with the exception of the horny Cliona, all the fossil sponges had originally calcareous skeletons,—"qu'ils n'ont jamais ÉtÉ cornÉs, mais que leur tissu a toujours ÉtÉ calcaire et pierreuse;"[196] which is certainly not the case, for abundant examples of fossil keratose sponges occur.

[196] Cours ElÉmentaire de PalÉontologie, torn. ii. p. 208.

I have selected a few genera for the illustration of the subject, and shall describe them under the names that are most familiar to the British scientific collector: doubtless sooner or later some competent naturalist will undertake the elucidation of this department of palÆontology, and construct a classification and nomenclature based on natural characters; till then the student will find it hopeless to attempt to learn the ever-varying names of genera and species applied to fossil Porifera and Polypifera, by different observers.[197]

[197] It has happened most unfortunately, that but recently Mr. Lonsdale, in the late Mr. Dixon's beautiful work on Chalk and Tertiary Fossils, and Mr. Milne Edwards in his able Monograph in the PalÆontological Society's Memoirs, have described many of our chalk Corals under different specific and generic names.

SPONGITES IN CHALK AND FLINT.

On the Sponges in Chalk and Flint.—From the durability of the tissue of the flexible sponges, and the imperishable nature of those which have a siliceous or calcareous endo-skeleton or framework, their fossil remains generally occur in a fine state of preservation, and in immense quantities, in the sediments that were deposited in those parts of the ancient sea-bottoms, originally inhabited by these zoophytes. Even the relics of the keratose species, the Halichondria, whose structure consists of siliceous spines imbedded in a cartilaginous mass, are equally abundant. Sponge-spicula are everywhere met with in the chalk, flint, and greensand, and many layers in the cretaceous strata are almost entirely composed of them.

Sponges so commonly form the nuclei of the nodular flints, that some naturalists have ascribed the formation of the layers and nodules of silex in the cretaceous rocks to these zoophytes: a supposition altogether groundless,[198] The various states of mineralization in which sponges occur in the chalk give rise to many beautiful and highly instructive fossils, as we shall point out in the course of this notice. In general the zoophyte is simply invested by the flint, the pores and tubes being filled with silex, the original tissue appearing as a brown reticulated calcareous mass. In other examples the sponge has been permeated by the liquid flint, and subsequently perished; and in this manner have been formed those hollow nodules which on being broken are found to contain only a powder, consisting of siliceous spicules and fragments of silicified sponge. But in numerous instances the substance of the zoophyte is completely silicified, and the intimate structure of the original exquisitely preserved; such are many of the flint-pebbles, and moss-agates, that are mounted as brooches and other ornaments.

[198] See Wonders of Geology, p. 300. This question is fully considered in a Memoir entitled Notes of a Microscopical Examination of the Chalk and Flint of the South-East of England, &c. by the Author, in 1845.

Spongites.[199]—This name I would apply generically to those fossils which appear to be identical in structure with the ordinary marine sponges that consist of a fibro-reticulated porous mass, destitute of regular tubes or canals: the form exceedingly various.

[199] Achilleum of Schweigger.

The fossil sponges of the chalk may be divided into two groups; the cyathiforms, or cup-shaped, and the ramose, or branched. Flints inclosing the first kind, generally exhibit externally the form of the original; those containing the branched species are of irregular shapes, and except by an experienced observer, the nature of the enclosed body would not be suspected. On breaking them, the sponge is often well displayed, as in the specimen figured in Lign. 69, fig. 2: the surface of this fossil was covered with a white gritty powder, made up of minute needle-shaped siliceous spicula.

SPONGITES IN FLINTS.

Spongites Ramosus.—A branched sponge, sometimes from twelve to fifteen inches long, is not uncommon in the flints of the Lewes and Brighton chalk; the stems and branches are cylindrical, and the terminations of the latter are rounded and full of large pores. When completely silicified the structure can only be detected by fracture, but occasionally the sponge appears to have been saturated with liquid chalk before it was enveloped in the flint; and as it is coated with calcareous matter, it may be detached from the nodule entire.[200]

[200] In this manner I obtained the beautiful specimen (now in the British Museum) figured in my Foss. South Downs, tab, xv. fig. 11. A branch of this species is represented Pict. Atlas, pl. xxxix. fig. 12.

Spongites lobatus (sp. Fleming) is figured Pict. Atlas, pl. xxxix. fig. 6.

Lign. 69. Coral, and Spongites.
Chalk. Sussex.

Fig.	1.—	Petalopora pulchella. Upper figure × ×: lower figure, nat. Chalk near Chichester. (Mr. Walter Mantell.)
	2.—	Spongites clavellatus. a branch in the cavity of a flint. South Downs.
	3.—	Siphonia Morrisiana. (G. A. M.) A transverse polished section of a pebble. Brighton Beach.

A smaller ramose spongite, with numerous short clavate protuberances, is often met with in the flints of Sussex and Wilts; a branch is figured in Lign. 69, fig. 2.[201]

[201] This spongite is named Polypothecia clavellata, in Miss Benett's Wiltshire Fossils.

Spongites Townsendi. (Pict. Atlas, pl. xli.)—The cyathiform flints, whose shape depends on the inclosed zoophytes, so much resemble the cup-shaped sponges of commerce, as to be easily recognized in the heaps of nodules that are collected in chalk districts for the roads; they are from one to eight inches in diameter at the upper part, and many are of a globular or spheroidal shape; the surface has the usual calcareo-siliceous coating of flint nodules, giving a sensation of roughness to the touch; the margin of the cup generally exhibits a narrow band of porous structure, and when broken, sections of the enclosed body are exposed. These funnel-shaped spongites terminate at the bottom in a peduncle, whence fibrous root-like processes diverge; by these appendages the original was fixed to the rock. I have collected a few specimens in which the roots are attached to a shell, or pebble, but have never seen any that appeared to occupy the spot on which they grew. They seem to have been detached from their native sites by the waves, and transported to a distance, and subsiding into the tranquil depths of the ocean, became imbedded in the cretaceous sediments that were accumulating at the bottom.

Spongites (?) labyrinthicus.[202] Lign. 80, fig. 5.—Another abundant species of amorphozoa has given rise to sub-hemispherical flints, rounded below and flat above, with a marginal band of porous tissue, that expands into flexuous lobes which fill up the area of the upper surface. When found imbedded in the chalk, the form of this zoophyte is often preserved entire; the upper part showing the lobated and flexuous character of the original. Upon breaking these flints, the organic structure is generally apparent; but in many instances has perished, and left a cavity which is either partially filled with stalactitical chalcedony, or lined with quartz crystals. These fossils vary in size from a walnut to that of an orange; the pedicle has long processes.

[202] Foss, S. D. tab. xv. fig. 7.

A lobed zoophyte, resembling the above in its general form, and long rootlets, is distinguished by a large central cavity, which is continued above the body in the form of a cylinder.[203]

[203] Beautiful figures of these and other chalk zoophytes are given by Mr. Toulmin Smith in his elegant memoir "On the VentriculidÆ." The specimens above described are named Bracholites by Mr. Smith. The plan of the present work forbids the discussion of that author's opinions and inferences.

Spongites (?) flexuosus. Lign. 80, fig. 10.—Among the cyathiform flints that abound in the chalk, a very elegant species is distinguished by a flexuous band that runs round the margin, and indicates the lobed structure of the original.

In the chalk of Flamborough Head, Yorkshire, many beautiful cyathiform sponges are preserved, in which the outer surface is thickly covered with projecting hollow papillÆ; these fossils are generally silicified, the surface and pores being frosted over with minute quartz crystals. The museum of the York Institution contains a splendid series of these spongites.[204]

[204] The silicified state of these zoophytes was first detected by Mr. Charlesworth, who by immersing specimens in dilate hydrochloric acid, obtained admirable examples of the delicate structure of the original.

FOSSIL ZOOPHYTES OF FARINGDON.

Fossil Zoophytes of Faringdon. Lign. 70, 71, 72.—The richest locality for fossil sponges in England is in the immediate neighbourhood of the little town of Faringdon, in Berkshire.[205] The Greensand beds that overlie the Oolite in that district, consist of a coarse friable aggregation of sand, comminuted shells, corals, amorphozoa, and echinoderms, more or less consolidated by a ferruginous cement. The gravel-pits, as the quarries are locally termed, expose what evidently were banks of detritus thrown up on the strand of a sea-margin; among the water-worn and fragmentary relics of oolitic as well as cretaceous forms, many perfect sponges of various kinds may be collected in the course of a few hours. Figures of some of the common species are subjoined.

[205] See Excursions, in vol. ii.

Lign. 70. Fossil Zoophytes.

Fig.	1.—	Lunulites radiatus. Preston Chalk-pits; view of the convex side. (Mr. Walter Mantell.) 1a.—Front view; nat. 1b.—Portion of the surface of fig. 1, magnified.
	2.—	Scyphia intermedia; 1/2 nat. Faringdon.
	3.—	Lithododendron sociale: the left-hand branch shows a vertical section at the upper part, displaying the internal structure; 1/2 nat. Mountain Limestone, Yorkshire.
	4.—	Verticillipora anastomosans. Faringdon.
	5.—	Scyphia ramosa; 1/2 nat. Faringdon.
	6.—	Scyphia foraminosa; 1/2 nat. Faringdon.
	7.—	Cnemidium astrophorum; 1/3 nat. Faringdon.

Scyphia. Lign. 70, 72.—These spongites are of a tubular, fistulous, or cylindrical form, and terminate in a rounded pit; they are either simple or branched, and composed of a firm reticulated tissue; Lign. 70, fig. 2, 5, 6, and Lign. 72, fig. 4, are examples. The Upper Greensand at Folkstone and Dover abounds in a flexuous species, named Scyphia meandrina (Morris).

Cnemidium (Goldfuss). Lign. 70, fig. 7.—These sponges consist of a cluster of turbinated projections, having a central pit above, and being porous on the external surface, and radiated at the margin. The mass is dense and fibrous, and is traversed by horizontal canals, diverging from the centre to the circumference.

Lign. 71. Fossil Sponge; nat.
(Chenendopora fungiformis.)
Greensand. Faringdon.

Chenendopora.[206] Lign. 71.—The species of porifera thus named are cyathiform, or cup-shaped; externally furrowed, mamillated, or lobed; internally smooth, and the surface covered with fine pores. The beautiful species figured (C. fungiformis) is abundant in the gravel-pits, and well known to the quarrymen as "petrified salt-cellars."

[206] The Pictorial Atlas contains coloured figures of the following:—

Chenendopora fungiformis (Michelin), Pict. Atlas, pl. xliv. fig. 5: according to Mr, Morris.

—————— subplana (Michelin), ibid, pl. xliv, fig. 3.

Scyphia articulata (Goldfuss), ibid, pl. xliii. figs. 7, 8, 9.

———- costata (Goldfuss), ibid. pl. xliv, fig, 1.

Cnemidium rimulosum (Goldfuss), ibid, pl. xliv. fig. 3.

Lign. 72. Fossil Zoophytes; nat.
Greensand. Faringdon.

Fig.	1.—	Tragos peziza.
	2.—	Probably Chenendopora in a young state.
	3.—	Verticillipora anastomosans.
	4.—	Species of Scyphia.
	5.—	Tragos Faringdoniensis.

Tragos. Lign. 72, fig. 1.—These turbinated sponges are readily distinguished from the preceding, by the relatively large oscula, or open papillÆ, disposed irregularly on the inner surface; as shown in the specimen, fig. 1. Their tissue is dense and fibrous. The fossil represented by fig. 5, though named Tragos by collectors, appears to differ in the structure of the inner surface from the type of this genus: it is a remarkably beautiful species.[207]

[207] It may be convenient to distinguish it as T. Faringdoniensis.

The base in all these Greensand sponges is flat and expanded; not fibrous and root-like, as in the spongites of the chalk previously described.

Among the shingle at Brighton, Margate, Dover, Isle of Wight, &c. pebbles containing fossil sponges may frequently be discovered. When the flint nodule has been broken, and the calcareous particles of the inclosed zoophytes are washed away by the action of the waves, a delicate silicified tissue remains.[208] Many of the large solid pebbles, are portions of silicified sponges, and polished specimens are beautiful objects under the microscope.

[208] The pebbles represented in Pict. Atlas, pl. xlv. fig. 5, 12, are specimens of this kind.

SIPHONIA.

Siphonia. Lign. 73.—These fossil porifera are readily distinguished from those which have engaged our attention by their more symmetrical structure. The body of the zoophyte is a mass of dense porous tissue, of a pyriform or bulbous shape, supported by a slender stem fixed at the base by rootlets. The stem is composed of very fine parallel longitudinal tubes, which extend to a series of canals that traverse the mass, and terminate in openings on the surface of a shallow central cavity, as shown in the section, fig. 2, Lign. 73. The characters of this genus are well exemplified in a common species of the Greensand (S. pyriformis, Lign. 73), described by the late Mr. Webster, from specimens collected in the Isle of Wight, where it occurs in profusion, near Ventnor, and the Western lines. This zoophyte is pyriform, (Lign. 73, fig. 1,) and has a shallow cylindrical cavity, supported upon a long slender stem, the base of which is fixed by root-like processes (fig. 5); the transverse fracture shows a section of the longitudinal tubes. This species has been found in numerous localities of the Greensand, and also in the Firestone or malm-rock.[209]

[209] Dr. Fitton's figures, Geol. Trans. vol. ii. pl. xv. a, are very beautiful and accurate.

The Portland limestone contains numerous remains of a Siphonia closely resembling this species; and varied sections of its stems produce the white markings commonly observable on the slabs of pavements.

Lign. 73. SiphoniÆ, from the Greensand; nat.
Wilts, and Isle of Wight.

Fig.	1.—	Siphonia pyriformis; the body or upper part.
	2.—	Vertical section of the same, showing the internal structure, and the central cavity.
	3.—	Specimen of S. pyriformis in a young state.
	4.—	Siphonia (Polypothecia, of Miss Benett,) lobata; Firestone or Upper Greensand, Warminster.
	5.—	The lower part of the stem, and radicles, of S. pyriformis.

A group of Sponges from the Upper Greensand, near Warminster, figured and described by the late Miss Etheldred Benett,[210] under the name of Polypothecia, comprises several forms that are allied in structure to the SiphoniÆ. These fossils present considerable diversity of shape; one of the lobed forms is delineated in Lign. 73, fig. 4: and a branched species in Lign. 74. Upon breaking the stem of one of these zoophytes transversely, sections of parallel longitudinal tubes like those in the SiphoniÆ are exhibited.

[210] An elegant Memoir on the Wiltshire Fossils, by this accomplished lady, is published in Sir R. C. Hoare's "Wiltshire."

Lign. 74.
Polypothecia dichotoma.
Upper Greensand, Warminster, Wilts.

The Kentish rag contains irregular ramose spongeous bodies, which belong to this group of porifera; and Mr. Bensted has discovered in his quarry, near Maidstone, numerous remains of a polymorphous lobed zoophyte, having a porous structure beset with spicula. In the Firestone of Southbourne, Steyning, and Bignor, in Sussex, I have observed large pyriform and subcylindrical SiphoniÆ.

The organization of all these zoophytes was evidently adapted for the imbibition and circulation of sea-water, in a more perfect and definite manner than in the irregular simple sponges.

Flint-pebbles inclosing remains of SiphoniÆ abound on the Sussex coast, especially in the shingle near Brighton, having been washed out of the chalk cliffs. There were several chalk-pits in Edward-street, (now, I believe, filled up and the area built upon,) in which every flint enveloped a sponge or siphonia; many specimens were mineralized by pyrites and beautifully exhibited the internal structure of the originals.

Siphonia Morrisiana. Lign. 69, fig. 3.—A polished slice of a pebble from Brighton, whose markings are derived from the transverse section of an undescribed zoophyte is figured, ante, p. 224.: though scarcely more than half the diameter of the original is preserved, yet its structure is well shown; the centre is occupied by numerous parallel openings, the sections of longitudinal tubes, and is surrounded by a broad zone of spongeous tissue.

I have seen many examples of this beautiful fossil, set for brooches in the jewellers' shops in the Isle of Wight, and at Brighton.[211]

[211] The specific name is in honour of John Morris, Esq. F.G.S. the author of the "Catalogue of British Fossils," whose important services to PalÆontology and Geology it is gratifying thus to acknowledge.

There are coloured figures of Siphonite in Pictorial Atlas, pl. xxxix. fig. 9; pl. xlii. fig. 3, 4, 5, 7, 12, and 13; pl. xliii. fig. 6.

SiphoniÆ (chiefly S. pyriformis) are abundant in the Upper Greensand, near Farnham in Surrey, but their tissues are saturated with phosphate of lime, instead of silica as is ordinarily the case; the entire sponge usually contains between 50 and 60 per cent, of phosphate: hence these fossils have, of late, been in great request for manure.[212]

[212] Mr. Payne, of Farnham, a distinguished agriculturist, has largely made use of them, both in the natural state and treated with sulphuric acid. The Firestone strata on St. Catherine's Hill, Isle of Wight, have been dug for a like purpose. See an "Account of the Phosphate Diggings," in my Isle of Wight, Second Edition, p. 448.

CHOANITES KÖNIGI.

Choanites KÖnigi, Lign. 75.—The zoophyte which has given rise to the fossils I have distinguished by the name of Choanites,[213] is of a spheroidal or sub-ovate form, and appears to have been composed of a softer tissue than the ordinary sponges. It has a central cavity, and was fixed at the base by long rootlets: its mass is traversed by numerous tubes or channels, which open on the inner surface of the cavity; it differs from Siphonia in not having a stem composed of bundles of tubes, and probably also in its constituent substance. Among the Sussex and Wiltshire chalk-flints specimens of this zoophyte are very common; they are easily recognized by the peculiar markings produced by the silicified tubes that radiate from the centre, as seen in Lign. 75, fig. 4. The semi-diaphanous pebbles on the Sussex coast, more frequently contain Choanites than any other zoophytes. From the beautiful and varied markings observable in the polished sections, they are in great request for brooches, and are termed petrified sea-animal flowers[214] by the lapidaries; among the shingle on the sea-shore at Bognor, Worthing, and other places, very fine examples may be collected.

[213] Foss. S. D. p. 178.[214] From the supposition that the original was an Actinia, or Sea-Anemone. A coloured vertical section of a pebble of this kind is figured in my "Thoughts on a Pebble," Eighth Edition, pl. ii. See coloured figures of Choanites in Pict. Atlas, pl. xlii. fig. 1, 9, and 10; pl. xliv. fig. 8; and pl. xlv. fig. 10.

Lign. 75. Choanites KÖnigi. (G. A. M.)
Chalk, Lewes.

Fig.	1.—	Transverse section of a siliceous specimen.
	2.—	Upper portion of a Choanite, in chalk, showing the opening of the central cavity at a.
	3.—	Vertical section of a Choanite, in flint, exposing a section of the mass, and canals passing obliquely from the central cavity, through the substance.
	4.—	Choanite in flint; the usual appearance of these fossils.
	5.—	Various kinds of Spicula of fossil sponges; magnified.

Lign. 75, fig. 4, represents the usual appearance of a flint deriving its form from a Choanite; fig. 2, is the upper part of a Choanite preserved in chalk, and richly coloured by iron; the opening at the summit, a, is the orifice of the central cylindrical cavity, which is in this instance filled up by chalk, but in flint specimens, with silex of a different colour to that of the surrounding mass. If fig. 2, were placed on the top of fig. 4, the general shape of the original zoophyte would be represented. The opening at the base of fig. 4, marks the spot whence the processes of attachment proceeded. The vertical section of a flint, similar to fig. 4, is shown at fig. 3; and in this example are seen the central cavity, and a section of the substance of the zoophyte, which is traversed by numerous tubes, that ramify through the mass of which the body was composed, and terminate in openings on the inner wall of the central cavity, or sac. A transverse section of a similar flint is delineated in fig. 1; the central white spot indicates the sac filled with flint, and the tubes are seen radiating from it through the mass; under a powerful lens the interstitial structure appears to be granular rather than porous. The perfect transparency of the body when silicified, and the rich tints it has acquired from metallic solutions, and the compressed state in which it is often found, seem to indicate that the original mass was a soft gelatinous substance, like that of the Actinia, strengthened by spicula; for numerous tri-radiate spines, like those on the left-hand of fig. 5, Lign. 75, occur occasionally in chalk specimens.

In many Choanites, which differ in no other respect from the present species, vertical sections show on each side the central cavity, large oval spots, that are sections of a canal which traverses the entire mass, proceeding from the base to the summit, in a spiral coil around the central cavity. This structure was first detected by Mr. Cunnington. Mr. Woodward thinks this spiral tube is common to all the Choanites, and constitutes a generic character; but so many examples have passed under my examination in which no traces of such a canal are perceptible, that it may be a specific difference.

Among the chalk amorphozoa whose true affinities are doubtful, is a small turbinated zoophyte, which I would place provisionally under this genus; it has a shallow central cavity, with a broad smooth margin, a reticulated external surface, and radicle processes proceeding from the base; see Lign. 80, fig. 1.

PARAMOUDRA.

Paramoudra. Lign. 76.—This vernacular Irish term was introduced by Dr. Buckland, in his account of some gigantic flints, thus popularly named, that occur in the chalk near Belfast, and also at Whitlingham, near Norwich. These fossils are of an irregular, oblong, spherical, or pyriform shape, having a cavity above, which, in some specimens, extends to the bottom; indications of a pedicle are seen at the base; in short, they closely resemble, upon a large scale, the funnel-shaped spongites, so frequent in the flints of the South Downs. Their appearance in situ, is represented Lign. 76, from Dr. Buckland's illustrations: b, is a single specimen, partly imbedded in the chalk, and c, d, two of the fossils in contact, the pedicle of the upper one lying in the cavity of the lower.

These bodies are from one to two or more feet in length, and from six inches to a foot in diameter. The appearance, both of the outer and inner surface, is that of the usual white calcareo-siliceous crust of spongitic chalk-flints. Upon breaking them, no decided structure is perceptible; but here and there, patches of red and blue chalcedony occur, as in the Ventriculites and spongites in chalk-flints; the originals were probably large goblet-shaped zoophytes, allied to the sponges, but of so perishable a nature as to leave but few traces of their organization, save their general form. Specimens may however yet be found with the structure preserved, for many years elapsed after the first discovery of flint ventriculites, before I obtained examples that threw light on their origin and formation.

Lign. 76. "Paramoudra;" seen in a vertical section of a Chalk-pit, near Moira.
(The Very Rev. Dr. Buckland. Geol. Trans, vol. iv.)

a, a, a.	Layers of flint nodules, alternating with chalk strata,
b.	A Paramoudra, imbedded in the chalk,
c, d.	Two of these bodies in contact.

In the Devonian slates of Polperro some curious fossils, supposed to be remains of fishes, have been ascertained by Prof McCoy to be Amorphozoa, and are described by that eminent palÆontologist under the name of Steganodictyum.[215]

[215] "Synopsis of the Classification of the British PalÆozoic Fossils," by Prof. Sedgwick and Fred. McCoy. 4to. Fas. 2, p. vii. pl. 2 A. 1852.

Clionites (Morris) Lign. 130.—A recent parasitical sponge (first described by Dr. Grant under the name of Cliona), consisting of a fleshy substance, full of siliceous tubular pin-shaped spicula, gives rise to those perforations with which oysters and other shells are often completely riddled,[216] Certain bivalve shells in the cretaceous seas appear to have been peculiarly obnoxious to the depredations of similar zoophytes, and in consequence of the cavities left by the decay of the sponge having subsequently been filled up by flint, a curious series of fossil bodies has resulted, which we shall more particularly notice hereafter. These fossils Mr. Morris has distinguished by the name Clionites, to indicate their origin; they are not, however, the silicified sponge, but inorganic casts, moulded in the excavations. The common species is C. Conybearei: "cells irregular, somewhat polygonal, with one or more papillÆ; surface finely tuberculated; connecting threads numerous."[217]

[216] For an account of the characters of the recent Cliona, see a monograph by Mr. Hancock, Annals of Nat. Hist. May 1851.[217] Ann. Nat. Hist. August 1851, pl. iv, fig. 8.

Spicula, or spines of Porifera. Lign. 75.—Siliceous spicules, as we have had occasion to mention, occur in immense quantities in some of those deposits which abound in the remains of spongites. These spines are tubular, and of various shapes; some are acicular, or needle-like; others of a stellate form; many are tri-radiate or multi-radiate; and some have the shape of a trident; a few of these fossils are figured in Lign. 75. As the Actinia, Gorgonia, and Alcyonia, possess spicula, some of the fossil spines may have been derived from those zoophytes. The larger spicules may be discovered with a lens of moderate power, or even by the unassisted eye; but all will amply repay a microscopical examination, and the minutest can only thus be detected.

SPINIFERITES IN FLINTS.

Lign. 77. A group of Spiniferites in Flint.
(Seen by transmitted light.)

Fig.	1.—	A thin-translucent chip of flint; nat.
	2.—	The same magnified, and viewed by transmitted light; showing a group of five Spiniferites.
	3.—	The same more highly magnified.
	4.—	Spin. ramosus; one of the animalculites seen in fig. 3, very highly magnified.
	5.—	Spin. Reginaldi; one of the same group; × 300 diameters.
	6.—	A variety of S. ramosus; another of the same cluster of Spiniferites.

Spiniferites (Xanthidium, Ehrenb.). Lign. 77.—I propose to describe in this place those elegant and very minute bodies, that occur in great numbers in the chalk and flint, and which, on the authority of M. Ehrenberg, were regarded as identical with the siliceous frustules of the genus of fresh-water DesmidiÆ, named Xanthidium[218] (ante, p. 91.) Later and more correct observations have proved that the fossils under consideration entirely differ from their supposed homologues; their original substance not being siliceous, but flexible and membranous; and that instead of being spores of algÆ, they are probably the gemmules either of porifera, or of polypifera.

[218] Several recent species of Xanthidium are figured in Plate IV. of this volume.

To avoid the perpetuation of the error by the retention of the botanical name of a recent genus of plants, for fossils whose vegetable origin is very problematical, and which are entirely distinct from their supposed analogues, I would substitute that of Spiniferites,[219] a term simply expressive of the general aspect of these bodies; that of a globe or sphere beset with spines. The appearance of these fossils will be understood by the examination of a group discovered by Mr. Reginald Neville Mantell, in a fragment chipped off from a flint pebble; and I will describe the mode by which these minute objects were detected, as it offers a good practical lesson for the young investigator.

[219] From spina, a spine, and fero, to bear.

The chip of flint is represented, of the natural size, in Lign. 77, fig. 1; it was immersed in oil of turpentine for a short time, and then placed on a piece of glass, and examined with a moderate power, by transmitted light, the turpentine having rendered the translucent flint almost as transparent as glass; this appearance is shown in fig. 2; the organisms here represented are from ¹/₃₀₀ to ¹/₅₀₀ of an inch in diameter. The half-inch object-glass was next employed, and fig. 3 gives the result. The quarter-inch object-glass, and a corresponding eye-piece, were then substituted, and by the adaptation of a camera lucida, figs. 4, 5, and 6, were delineated. As fig. 5 proved to be a new species, it was named after its discoverer.

The specimens in flint, when rendered transparent and viewed by transmitted light under a high power, as shown in Lign. 78, and 79, appear as hollow globular bodies, beset with spinous processes, which in most species are fimbriated at the extremities. There is considerable variety in the form and length of the spines. In S. Reginaldi, these appendages are numerous, regular, short, and relatively thick: in an elegant species discovered by the Rev. J. B. Reade (Lign. 79) they are long and palmated: in other kinds they are of intermediate size and proportions.[220]

[220] Excellent figures of several species are given in a Memoir by H. H. White, Esq. of Clapham, in the Trans. Microscopical Society, vol. i. p. 77.

Lign. 78. Spiniferites Reginaldi. (Magnified 500 diameters.)	Lign. 79. Spiniferites palmatus; in flint. (× 500 diameters.)

The apparently torn and collapsed state of the body and arms of some examples first led me to doubt the siliceous nature of the original substance; and on my discovery of the soft parts of foraminifera in flint and chalk, Mr. Deane undertook to search for the so-called Xanthidia in chalk, that these bodies might be subjected to chemical analysis,[221] Mr. Deane succeeded in detecting all the usual species in the Dover chalk, by digesting some chalk in dilute hydrochloric acid, and mounting the residue in Canada balsam. In this state the shape of the body is that of a depressed sphere; many of the specimens appear to have a circular opening, and the arms or spines to be closed at the extremities. Upon pressure under water between two pieces of glass, they were torn asunder as a horny or cartilaginous substance would be, and the spines in contact with the glass were bent. Some after maceration in water several weeks became flaccid; a proof that they are not siliceous.[222]

[221] A torn and apparently shrunken specimen from chalk, is represented in my paper on Foraminifera; Philos. Trans. 1846, p. 465.[222] Memoir on Fossil Xanthidia, by Henry Deane, Esq. Microscopical Journal, 1846.

The real nature of these fossils must be regarded as still undetermined: their prevalence in the chalk-flints whose forms are derived from zoophytes, seems to countenance the supposition that the Spiniferites are the gemmules or early state of animals of this family; but I have never detected any organic connexion between them and the porifera with which they are associated; it is possible they may be the germs of the remarkable zoophytes we have next to examine.

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VENTRICULITES.

Ventriculites.[223] Lign. 80, 81, 82.—At every step of our review of the fossil zoophytes, I find myself embarrassed by the conflicting opinions entertained by naturalists, respecting some of the most abundant of the extinct forms; arising from the imperfect state of our knowledge as to the structure of the originals, which compels a comparison with recent types, from which, perhaps, the fossils differed essentially in their organization. This remark especially applies to the zoophytes which have given rise to the fungiform flints so well known to the inhabitants of the chalk districts of Sussex, as "petrified mushrooms," from their close resemblance in form to fungi: a specimen with this name inscribed on it in the cabinet of a friend first drew my attention to these curious fossils. In Lign. 80, figs. 2, 3, 4, 6, 7, 8, 9, several flints of this kind are represented; figs. 3, 6, 8, are fungiform; fig. 7, is the upper part of a specimen, the stem having been broken off; figs. 2 and 4, are examples of the lower part of the zoophyte; in all, there are openings at the base, and a groove on the margin or edge of the upper part in which the structure of the inclosed fossil is visible; upon breaking these flints, sections of a funnel-shaped body are exposed.

[223] Ventriculite; from ventriculus, a ventricle or sac.

Lign. 80. Flints, deriving their forms from Zoophytes.
From the South Downs, near Lewes; ¹/₆ nat.

Fig.	1.—	Choanites (?) Turbinatus.
	2,3,	4, 6, 7, 8, 9.—Flints, whose forms are derived from Ventriculites, provincially called "petrified mushrooms."
	5.—	Spongites labyrinthicus.
	10.—	Spongites flexuosus.

The origin of these fossils will be understood by reference to the four specimens delineated in Lign. 81. In fig. 3, a fungiform flint, resembling fig. 6, of Lign. 80, is seen in the lower part of a cup-shaped zoophyte; while above, and surrounding the flint, the impression remains of the reticulated outer surface, deeply coloured by a ferruginous tinge. In fig. 4, Lign. 81, a small turbinated flint, resembling fig. 4, of Lign. 80, occupies the base, and three rootlets are seen emerging from it at a. In Lign. 82, fig. 1, in which the chalk has been removed so as to expose the outer surface of the Ventriculite, a flint occupies the centre at c; above which, the radiating reticulated structure is spread out on the chalk, a; the base, with its roots, is shown at b.

Lign. 81. Ventriculites radiatus; ¹/₆ nat.
Chalk; near Lewes.

Fig.	1.—	A perfect specimen in chalk, inverted, showing the external reticulated surface; the apex of the base projects in the centre.
	2.—	Specimen expanded, displaying the inner surface, studded over with the openings of the cells or tubes.
	3.—	A Ventriculite in chalk; the lower part inclosed in flint.
	4.—	Portion of a Ventriculite; the stem towards the base is enveloped in flint, and three radicle processes spread from it into the surrounding chalk at a.

These specimens demonstrate that all the flints referred to, have been moulded in the cavities of cyathiform zoophytes; and that their diversity of figure has arisen from the amount of silex that happened to permeate the organism; if but a small proportion of silica in solution was present, then flints, like fig. 4, were produced; if the quantity were sufficient to fill up a considerable part of the tissues of the original, fungiform flints, as Lign. 80, fig. 3, and Lign. 81, fig. 3, were the result. The disciform flints originated from the expanded examples, Lign. 81, figs. 1 and 2: and when the silex was insufficient to silicify the entire zoophyte, an annular flint, resembling a quoit, was formed.

Lign. 82. Portions of Ventriculites; ¹/₄ nat.
Chalk, near Lewes.

Fig.	1.—	A specimen, in which the middle is inclosed in a flint c; the external structure of the Ventriculite is seen at a, expanded on the chalk; and the pedicle with its roots is exposed at b. The figures are one-fourth the size of the originals.
	2,3,	5.—Chalk specimens, showing the external structure of stems of Ventriculites.
	4.—	A siliceous cast of the cavity of a Ventriculite covered with papillÆ, moulded in the orifices of the cells.

The form of the original was evidently that of a hollow inverted cone, terminating in a point at the base, which was attached by fibrous rootlets to other bodies. The outer integument was reticulated, that is, disposed in meshes, like net-work; and the inner surface studded with regular openings, apparently the orifices of tubular cells. The substance of the mass appears to have been sufficiently flexible to expand and contract without laceration. This opinion is based on the fact, that in many specimens the zoophyte is a nearly flat circular disc (Lign. 81, figs. 1, 2); and in others a subcylindrical pouch. In the former state the outer reticulated structure is elongated, while in the latter, it is corrugated; hence I am led to conclude that the original possessed a common irritability, and was able to contract and expand like many of the flexible polypiaria. The openings on the inner surface are cylindrical, and very regular; the flints often present sharp casts of them, which appear like rows of minute pillars. When the flint filling up the cavity of a Ventriculite can be extracted, it is a solid cone, studded with papillÆ, the casts of the cells, as in Lign. 82, fig. 4.

In the flints, the substance of the Ventriculites is generally as translucent as that of the Choanites, and defined by its rich purple, sienna, or grey colour;[224] but towards the base and margin it is more or less calcareous; and in many examples the whole, or a large portion of the zoophyte, is in this state. But this fact does not invalidate the inference that the original was flexible; for in these instances the tissues may have been immersed in fluid chalk before their envelopment in flint,[225] The chalk specimens are commonly as friable and earthy as the surrounding stone, from which they are distinguishable by their ochreous colour.

[224] Pict. Atlas, pl. xlv. fig. 9, represents a beautiful transverse section of the lower part of a Ventriculite in flint, richly coloured. Pl. xliii. fig. 16, is a pebble containing the base of a Ventriculite; the orifices on the top have been produced by the transit of the radicle processes; for the fossil is drawn in an inverted position, a common error before the origin of these flints was ascertained.[225] A piece of sponge dipped in liquid plaster of Paris, and afterwards inclosed in a transparent substance, as glass, would present such an appearance.

The stain always observable in the tissues of the chalk Ventriculites and other zoophytes, while the surrounding white limestone is uncoloured, may be explained by the chemical changes to which the decomposition of animal matter under such circumstances would give rise. If sulphuretted hydrogen were evolved from the putrifying zoophytes imbedded in calcareous mud containing iron in solution, the sulphur would enter into combination with the iron, the hydrogen escape, and a sulphate or sulphuret of iron be deposited, atom by atom, and thus impart colour and permanence of form to the original.

When the inclosed organisms in the flint nodules have perished, chalcedony, quartz crystals, or crystallized pyrites, sometimes of great beauty, are found occupying the cavities; in short, numerous modifications of the petrifactive process are beautifully exhibited in these common, but highly interesting, cretaceous fossils.

The species to which the previous remarks more immediately refer, is named Ventriculites radiatus; from the radiated appearance of the external integument; some of the expanded specimens are more than one foot in diameter.[226]

[226] The reader interested in the history of these objects should consult Foss. South Downs, p. 167, plates x, xi, xii. xiii. xiv. A memoir by the Author on these fossils, under the name of Alcyonium chonoides, with four beautiful plates, was published in the LinnÆan Transactions, vol. xi. 1821. The Ventriculites are the only organic remains figured in Conybeare and Phillips's Geology of England and Wales, p. 76.

Lign. 83. Ventriculites alcyonoides. in Flint. Lewes.
Ocellaria inclusa. KÖnig.

Fig.	1.—	Portion of the surface of fig. 2, magnified.
	2.—	The fossil body extracted from the flint, fig. 4. 2a.—Transverse section of the same, showing a central spot of flint, surrounded by tubular cells. 2b.—Two of the cells of fig. 2a, highly magnified.
	4.—	The hollow flint, from which fig. 2 was extracted; the papillÆ on the surface, are casts of the apertures of cells.

Ventriculites alcyonoides. Lign. 83.—Under the name of "Ocellaria inclusa," the late Mr. KÖnig[227] figured and described an elegant fossil zoophyte not uncommon in the chalk and flints of Sussex. This fossil is inversely conical, and somewhat resembles the cast of the cavity of Ventriculites radiatus, but a little attention will enable the collector to distinguish it. The flint that is moulded in V. radiatus, is surrounded by the substance of the zoophyte, and if found detached, with the investing material removed, shows no structure whatever, but simply a surface covered with minute papillÆ. The present zoophyte is generally included in a nodule, and by a slight blow may be readily separated from the surrounding flint; it then has the appearance of a white calcareous cone, beset with regular cells, disposed in quincunx order (Lign. 83, fig. 2); leaving a conical cavity in the flint, which is covered with corresponding eminences (Lign. 83, fig. 4). Upon breaking the cone itself, it is found to consist of a dense reticulated structure, from one-eighth to a quarter of an inch in thickness (Lign. 83, fig. 2a), investing a solid nucleus of flint, the surface of the latter being covered with minute points, which are less regular than those on the cavity of the outer case. The specific name, inclusa, was suggested by this character; which, however, is only accidental, for the specimens imbedded in chalk, are simply surrounded by the stone. It is the calcareous nature of the fossil, which renders it so easily separable from the investing flint, while its cells afford numerous points of attachment, and these remain as casts in relief on the interior of the hollow case: I have not observed the same regularity of structure on the inner as on the outer surface.

[227] Icones Foss. Sect. fig. 98.

The reticulated integument of this zoophyte resembles in structure that of V. radiatus. With regard to the latter, I should state that Mr. Toulmin Smith[228] discovered that the inosculating fibres of the intimate tissue formed an octahedral plexus at each knot or point of union; and this structure Mr. Smith regards as peculiar to the Ventriculites, and states that he detected it in all the fossils he has arranged under the name VentriculidÆ. No spicula have been detected in the integuments.

[228] "On the VentriculidÆ;" a series of papers published in the Annals of Natural History, with many figures of cretaceous zoophytes. By Toulmin Smith, Esq.

Until more ample and satisfactory evidence is collected as to the nature of these fossils, the interests of science will be best promoted by allowing the question to remain sub judice, and restricting the term Ventriculites to those zoophytes which possess the general characters of the type to which the name was originally assigned; namely, a vasiform or subcylindrical framework, terminating at the base in a point, and fixed by radicle processes; the substance consisting of a plexiform fibrous tissue; externally constituting a reticulated integument, the meshes disposed in a radiating manner from the base to the periphery; the inner surface studded with open cells regularly arranged.

In the former edition of this work the Ventriculites were placed with the Polypifera from the structure of the openings or cells, for these are so symmetrical, and disposed with so much regularity, as to present a closer analogy to the polype-cells of a coral, than to the large pores of a sponge. The doubts expressed by many eminent observers as to the correctness of this view, have induced me to insert this notice in the present section; leaving the true affinities of these organisms to be determined by future observers. Possibly we have in these fossils the relics of a tribe of zoophytes of an extinct type, that formed a connecting link between the porifera and the polypifera; however this may be, I will venture to affirm that no one who had seen the infinitely varied examples of these fossils that I have, would for a moment confound them, as some naturalists have done, with the ScyphiÆ, and other simple amorphozoa.

Lign. 84.
A Coral-polype in flint.
× 500 diameters.
(Seen by transmitted light.)

Polype in Flint. Lign. 84.—I will here notice an exceedingly minute and interesting object, discovered by the Rev. J. B. Reade, in a flint containing vestiges of a Ventriculite, and which may possibly belong to this tribe of zoophytes. It must however be remarked, that there was nothing to show the collocation was not accidental. The drawing with which Mr. Reade favoured me, is engraved Lign. 84. This object is unmistakeably a polype-cell, with some of the integument of the animal protruding, in the form of a shrivelled tube. The possibility of soft animal tissues being preserved in flint, will not now admit of question, as we shall show when treating of the Foraminifera. The record of this fact may load to the discovery of other fossils of a like nature.

Fossil Polypifera.

POLYPIFERA.

As we proceed in our investigations, the impossibility of rigidly adhering to a zoological classification based on the structure of organs, of which but few, if any, traces exist in the mineral kingdom, becomes more and more apparent; the durable skeletons or polyparia being the only materials from which the palÆontologist can gather information, relating to the physiology of the extinct coral-animals which swarmed in the ancient seas, and whose petrified remains constitute a large proportion of the secondary and palÆozoic calcareous rocks.

Numerous fossil genera have been established by various authors from the external form of the polyparium, or the disposition and structure of the cells; but a slight attention to this department of palÆontology will disclose corals which differ essentially from the typical forms, and new genera and species will require to be added to the already extended catalogue. The few genera selected for the present work, will convey a general idea of the nature of this class of fossils. To ascertain the names of the species he may collect, the student must refer to works especially devoted to the illustration of the corals of particular rocks; as for example, those of the British Cretaceous deposits in the monographs of the PalÆontological Society; of the PalÆozoic in Sil. Syst.; and in Prof Sedgwick's Synopsis of the Classification of the Brit. Pal. Foss.; of the Mountain Limestone in Prof, Phillips's work; and those of Ireland in Col. Portlock's Geological Memoirs. Those of the palÆozoic rocks of New York, are illustrated in Prof. James Hall's splendid work on the Geology of that State.

The fossil zoophytes included in this section present innumerable varieties of form and structure, but agree in the important character of having originated, (with but few exceptions,) from aggregations of those minute beings termed Polypes (many-feet[229]). The common Hydra (Wond. p. 600), or fresh-water polype, that inhabits pools and streams, is a familiar example of a free animal of this kind, consisting of a cellular gelatinous substance, in the form of a short tube, or pouch, surrounded at the upper margin by long tentacula, or feelers, which appear to the naked eye as delicate threads. The Polypifera, properly so called, are groups of polypes, permanently united by a common integument or axis, each animalcule having an independent existence. A common support or endo-skeleton, termed polyparium,[230] is secreted by the integuments, which varies in its nature from a mere gelatinous, or horny material, to an earthy, calcareous, and even siliceous substance, that remains when the polypes die, and their soft parts have perished. All the varieties of corals, &c. are nothing more than the durable structures of aggregated masses of such beings.

[229] A name derived from the tentacula, or processes, which in some species serve for prehension, and in others for respiration.[230] The basis, framework, or endo-skeleton, of these groups of animalcules is termed the polyparium, or polypidom (polype-habitation); those of a stony hardness are familiarly known as corals; these names, therefore, refer to the durable substance, and not to the animals themselves; but in familiar writing, the term Coral is often used to designate the entire living mass. The Red-Coral forms a distinct genus called Corallium. In fossils, the polyparium alone remains, except in very rare instances.

It may here be necessary to notice a prevailing error, regarding the mode in which the substance called coral is produced. It is very generally supposed that Corals, particularly those bearing stars and cells, have been constructed by animalcules, in the same manner as is the honey-comb, by the Bee; and the expressions often employed by naturalists, of "the coral animalcules building up their rocky habitations," and "constructing their cells," have contributed to foster this error. But the processes are in no respect similar: the insect, under the guidance of an unerring instinct, resulting from its peculiar organization, constructs its cells; but the polype is incapable of forming, or even modifying, its support or cell in the slightest degree. The polypidom is secreted by the animal tissues, in the same manner as are the bones in the vertebrated animals, without the individual being conscious of the process. If a piece of white coral be immersed in dilute hydrochloric acid, the calcareous part is dissolved, and the secreting membrane, in the form of a flocculent substance, is seen attached to the undissolved part; even in some coralline marbles of incalculable antiquity, the animal membrane may, in this manner, be detected.[231]

[231] See Pict. Atlas, pl. xxxiv. fig. 2.

From the delicate and perishable nature of many of the gelatinous zoophytes, numerous tribes may have inhabited the seas, which deposited the fossiliferous strata, and yet no indications of their existence remain; while, of others, but obscure traces of their structure are likely to be detected.

The Polypifera are separated into two natural groups or classes; viz. the Anthozoa (flower-animals), and the Bryozoa (moss-animals), or Polyzoa.

The Anthozoa are polypes of the most simple type of structure. The body consists of a symmetrical gelatinous sac, capable of contraction and expansion, with one aperture or mouth, which is encircled by tentacula. The Hydra, or fresh-water polype (Wond. p. 600), is a familiar example of a single, locomotive, anthozoan animal. In the compound or aggregated forms, the body is either inclosed in a horny sheath (ex. Sertularia, Wond. p. 615), or is supported by a lamellated calcareous endo-skeleton (ex. Fungia, Wond. p. 623, pl. vi. fig. 15), or the soft parts invest a stony axis (ex. Madrepora, Wond. p. 620), or a horny flexible framework (ex. Gorgonia, Wond. p. 616).

The Anthozoa are subdivided into three orders, which are based on the peculiar characters of the polypes; the Hydra, the Actinia (Sea-Anemone, Wond. p. 622), and the Alcyonium (Dead-men's fingers, Wond. pl. v. fig. 10), being respectively the type of 1. the Hydroida, or Hydraform; 2. the Asteroida or Alcyonian; and 3. the Helianthoida, or Actiniform zoophytes.

In the Hydroida the body in the compound species is implanted in a horny tubular sheath, and the polypidoms form branched corallines, which are fixed by the base to rocks, sea-weeds, shells, &c.

The Asteroida have a horny or calcareous axis, surrounded and inclosed by the soft parts which secrete it.

The Helianthoids, except in the simple free species, as the Actinia, have a lamellated calcareous polypidom, the plates of which radiate from a centre.

The calcareous secretions of the Anthozoa, especially of the Helianthoida, in a great measure constitute the mass of the coral-reefs and coral-islands of tropical seas. Their polypidoms, whether external or internal, maintain but little organic connexion with the compound soft substance. These zoophytes increase by gemmation or budding; some throw up germs from the disk, as in AstreadÆ; others laterally, as in CaryophillidÆ; and some spirally along the stem, as in MadreporidÆ; examples of these modes of reproduction are often found in fossil corals. The increase of coral-rocks is produced by the continual formation of new masses, by the successive generations which spring up as it were from the bodies of their parents; layer upon layer, and tier upon tier, of Helianthoid polypidoms, are found to compose many of the coralline limestones of the palÆozoic formations.

Fossil Anthozoa.—The first group of extinct corals to be noticed under this head is the GraptolitidÆ, a family restricted to the Silurian rocks, and whose natural affinities have been much questioned; some palÆontologists referring them to the PennatulidÆ, or Sea-pens, others to the SertulariadÆ.[232]

[232] For a full consideration of this subject, refer to Prof. McCoy's Brit. PalÆozoic Fossils.

GRAPTOLITES.

Lign. 85. Graptolites in Wenlock Limestone.
(Murch. Sil. Syst.)

Fig.	1.—	Graptolites ludensis.[233]
	1a.—	Magnified view of a portion of the same.
	2.—	Graptolites Murchisoni.
	2a.—	Magnified portion of fig. 2.

[233] Ludensis, from Ludlow—to indicate the habitat of the fossils.

Graptolites. Lign. 85.—These curious zoophytes abound in many of the Silurian deposits; they consist of sessile polype cells, arranged in one or two rows to a flexible stem, like the recent Sertularia, or Virgularia. Prof. McCoy refers them to the order Hydroida.

In a recent state these bodies were probably covered with a soft, or albuminous mass, studded with polype-cells, disposed in rows along the margins of the lateral, curved, grapple-like processes, as in the zoophytes termed Virgularia,[234] to which one kind bears a great analogy. If two specimens of the Graptolites Ludensis be placed together, so that the elongated smooth edges be in apposition, the united stems will be seen to offer a general resemblance to the axis of Virgularia mirabilis.

[234] See British Zoophytes, pl. xxiv.

M. Barrande divides the Graptolites into three groups or genera, which are defined as follow:—

Graptolites (proper), a single series of cells united together at the base, and adhering along the sides nearly to the orifice of each cell, as in fig. 1a. Monoprion of M. Barrande.

Rastrites.—The axis reduced to a mere line, on which the cells are placed at relatively wide intervals, and but slightly inclined. These two genera are supposed to have been hydroid zoophytes, and related to the SertularidÆ.

Diprion (Diplograpsus of Mr. McCoy), cells in two series arranged along a central axis; these forms present a foliaceous appearance; they are presumed to resemble the existing genera Pennatula and Virgularia.

Graptolites have been found in strata of the same age in Norway, Sweden, and Scotland.[235] I have received slates literally covered with them, from the Silurian rocks of the United States, by the kindness of my friend, Benjamin Silliman, jun. Esq.

[235] Many species of Graptolites from the Lower Silurian rocks of the South of Scotland, are described and figured by Mr. Harkness in Geol. Journal for 1850, vol. vii. p. 58, pl. 1.

Sir R. Murchison remarks, that the nature of the strata in which these remains occur in Radnorshire, indicates a condition of the sea, well suited to the habits of the family of PennatulidÆ, or Sea-pens; for the recent species live in mud and slimy sediment, and the fossils are imbedded in a finely levigated mud-stone, which, from its structure, must have been tranquilly deposited.

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I will next describe the single lamellated Anthozoa, and afterwards notice those corals which consist of an aggregation of radiated cells, either frondescent, or disposed in solid masses.

FUNGIA. ANTHOPHYLLUM.

Fungia (Wond. p. 623).—The corals thus named, from their supposed resemblance to fungi, are of a depressed form, and have the under surface scabrous; they are divided above by numerous lamellÆ, or plates, which radiate from a central, oblong depression.

When living, the solid stony polyparium is enclosed in the gelatinous mass by which it was secreted, and there are numerous tentacula around the central cavity, or sac. These zoophytes may be compared to the ActiniÆ, or Sea-Anemones, from which they differ only in having a calcareous axis, while the ActiniÆ have a tough albuminous integument. (Wond. pl. vi. fig. 15, represents the living animal; and Lign. 141, fig. 2, p. 641, and Lign. 58, fig. 4, two fossil species).[236]

[236]

Fungia numismalis. Pict, Atlas, pl. xxxvi. fig. 6.
——— polymorpha. Ibid. pl. xliii. fig. 1—4; pl. xlv, fig. 11.

Anthophyllum Atlanticum. Lign. 88. fig. 4.—In the arenaceous strata of the United States, which the researches of Dr. Morton, of Philadelphia, have proved to be the equivalents of the European Cretaceous formation, a single lamellated coral is not uncommon. It is evidently related to the FungiÆ, and has been named as above by Dr. Morton.

Turbinolia KÖnigi (Wond. p. 320).—Polyparium turbinated, striated externally, detached, base not adhering; cell single, radiated.

This genus occurs in all the fossiliferous deposits: a small, well-marked species is frequently met with in the Galt, of which subdivision of the cretaceous strata it is a characteristic fossil. It is figured Wond. Lign. 58, figs. 1, 2.[237]

[237]

Turbinolia complanata. Ibid. pl. xxxvi. fig. 9.
————— mitrata. Ibid. pl. xxxvi. fig. 10.

Caryophyllia centralis (Lign. 89 figs. 1, 2: Lign. 88, fig. 5).—Polyparium turbinated, or cylindrical, simple or branched, longitudinally striated, fixed by the base; cells lamellated.[238]

[238] Monocarya (of Lonsdale), Dixon's Fossils, p, 244.

A small recent species (C. cyathus), is very common in the Mediterranean, and frequently seen in collections: it is cyathiform, and the base by which it is attached to other bodies, is broad and spreading; the newer tertiary deposits of Sicily contain this species in abundance.

A Caryophyllia, bearing a general resemblance to this species, is common in the chalk, and occurs in beautiful preservation (Wond. Lign. 58, fig. 3).[239]

[239]

C. centralis, Pict. Atlas, pl. xxxvi. figs. 15, 16.
C. annularis, ibid. pl. xxxvii. fig. 5.

Branched CaryophylliÆ are found in the Coralline Oolite and Dudley Limestones (Sil. Syst. pl. xvi.). A large proportion of the Coral-rag of the Middle Oolite is composed of a branched species (C. annularis) of this genus; Lign. 88, fig. 5, represents a specimen from near Faringdon.

Lign. 86. Favosites polymorpha. (Goldfuss.)
Devonian limestone. Eifel.

Fig.	1.—	Portion of a branch of the coral; nat.
	2.—	Fragment, slightly magnified, with part of the surface broken away below, exposing the central axis, and radiated arrangement of the cells, with their lateral pores.
	3.—	Another portion, magnified, showing the polype-cells hollow.

Favosites polymorpha. Lign. 86. Lign. 88, fig. 3.—Polyparium stony, polymorphous, solid internally, compact, composed of a congeries of diverging or ascending parallel, contiguous, prismatic tubes, covered by pores, divided by lamellÆ, and communicating by lateral foramina.

The corals of this extinct genus abounded in the Silurian and Devonian seas; the remains occur with those of other fossil zoophytes of that epoch in great numbers, both in Europe and North America. I have many beautiful examples from the Silurian rocks of the Ohio and Niagara, by favour of Dr. Owen, of New Harmony, and Dr. Yandell, of Louisville, in which the cells are filled up with calcareous spar. The varied markings on many of the Babbicombe marbles, and Torquay pebbles, are derived from the enclosed Favosites (Wond. p. 643).

Another species (Favosites Gothlandica) occurs in masses of a subconical shape, and is common in some of the Silurian limestones. A fragment, to show the structure, is figured Lign. 88, fig. 3.

CATENIPORA. SYRINGOPORA.

Catenipora (Wond. p. 644, fig. 3).—Polyparium hemispherical, composed of vertical anastomosing lamellÆ; cells tubular, oval, terminal, united laterally. The oval form of the cells when united laterally, and the flexuous disposition of the lamellÆ, give rise in transverse sections to elegant catenated markings, from which appearance the fossil has received the name of chain-coral.[240] The species figured (C. escharoides) in Wond. is common in the Silurian limestones, and sometimes forms hemispherical masses more than a foot in diameter. The chain-coral is extensively distributed through the Silurian rocks of the United States. Coloured figures of this exquisitely beautiful coral are given in Pict. Atlas, pl. XXXV.

[240] Org. Rem. vol. ii. pl. iii. figs. 4, 5, 6.

Syringopora ramulosa. Lign. 88, fig. 2. (Wond. p. 641.) These corals bear a general resemblance to the Organ-pipe Coral of Australia. The polypidom is composed of long, cylindrical, vertical tubes, distant from each other, and connected by transverse tubular processes; the cells are deep and radiated by numerous lamellÆ.

The external aspect of these fossils is that of a cluster of cylindrical pipes, more or less parallel, connected by short transverse branches. They are the Tubiporites of Mr. Parkinson, who has given admirable figures of several specimens.[241] In these fossil corals that excellent observer first detected the animal membrane. A slab of marble, whose markings are produced by the section of the inclosed tubes of a Syringopora, is represented, Wond. p. 644, fig. 2. The Mountain limestones of Derbyshire, and of Clifton, on the banks of the Avon, contain figured marbles of this kind, which are manufactured into vases, tables, &c. The genus is extinct.

Lithostrotion Columnaria (Wond. p. 641, fig. 8).—Polyparium massive, solid, composed of aggregated, contiguous, parallel, prismatic tubes, each terminated by a star: cells shallow, multi-radiate, stelliform.

Species of this extinct genus are common in the mountain limestone, in large masses, which, from the pentagonal form, and parallel arrangement of the tubes, appear like clusters of miniature basaltic columns.[242]

Cyathophyllum. Lign. 87, figs. 1, 2. (Wond. p. 641, figs. 1, 3.)—Polyparium turbinated, simple or compound, internal structure transversely chambered or lamellated; cells polygonal, radiated, depressed in the centre.

The corals of this genus are so abundant in the Silurian rocks, that the seas of that epoch must have swarmed with them. The simple turbinated forms are often several inches long, and being somewhat curved, have obtained the popular name of "petrified rams-horns."

Upon slitting one of these corals vertically, as in Lign. 87, fig. 1, the axis of the polyparium, beneath the cell, is found to consist of thin transverse partitions, constituting a series of chambers.

In the compound Cyathophylla, the germs of young cells, occupying the disc of a parent cell, are often met with. Fig. 3 represents a group of four germs on the parent cell, of C. dianthus, a common and beautiful coral of the Dudley limestone.

These corals are also prevalent in South Devonshire, and many of the elegant marbles of Babbicombe are figured by the sections of these polyparia.[243]

Associated with the Cyathophylla in the Silurian rocks, are certain corals that attain considerable magnitude, and which are principally distinguishable by their internal structure. Such are Cystiphyllum, constructed of bladder-like cells, and Strombodes, composed of spirally contorted lamellÆ, or plates (Sil. Syst. pl. 16⁽bis), fig. 4). Other hemispherical masses, presenting on the surface concentric wrinkles, with very minute pores, are common at Dudley, and belong to the genus Stromatopora.

Astrea. Lign. 88, figs. 1, 1a.—Polyparium massive, irregular in shape, generally globular, formed by an aggregation of lamellated, radiated, shallow, polymorphous cells.

The corals of this genus are very numerous in the seas of the Tropics, and there are many species in the Oolite, and older secondary formations. The AstreÆ, CaryophylliÆ, Cyathophylla, &c., form the principal mass of the coralline limestones of the Oolite, termed the Coral-rag, from the abundance of these relics: being literally composed of an aggregation of large corals, the interstices of which are filled with shells, radiaria, &c., either whole, or in a comminuted state. The heaps of this limestone placed by the road-side, in the N. W. of Berkshire, appear like fragments of an old coral-reef, and attract the notice even of the most incurious observer. I have figured a specimen of Astrea, Lign. 88, fig. 1, and a polished section, fig. 1a, from Clifton, a locality well known for the stupendous mural precipices of mountain limestone rocks, which yield beautiful examples of coralline marble.[245] The mode of increase of the Astrea is very curious; a subdivision takes place in the old cells, after the manner of the Infusoria; and among the fossils, a star or cell may often be seen in progress of division into two, three, or four stars (Sil. Syst. pl. xvi. fig. 6). A living polype of this genus is figured, Wond. pl. vi. fig. 13.

A species of Astrea (A. Tisburiensis. Wond. p. 641, fig. 9), is found in large hemispherical masses, completely silicified, at Tisbury, in Wiltshire. The transverse surface displays, in some specimens, beautiful white radiated stars, on a dark blue ground; and in others, the colours of the stars and ground are reversed. This silicified coral is obtained from a bed of chert, a foot in thickness, which is interstratified with the Portland limestone, this division of the Oolite being quarried around Tisbury.[246]

In the tertiary clays at Bracklesham Bay, Sussex, a beautiful small coral of this type (Siderastrea Websteri, Dixon's Foss. tab. i, 5), is found attached to flint pebbles.

Several species of this and the following genus, perfectly silicified, are found in the state of pebbles and boulders in the superficial soil of Antigua, and other islands of the West Indies, associated with the fossil palms, described in a former part of this work. Some of these corals are of great beauty, and polished sections exhibit the coralline structure most perfectly.[247]

Madrepora.—Polyparium arborescent or frondescent, porous, fixed; cells deep, with twelve rays, prominent, irregularly dispersed on the surface, and accumulated towards the terminations of the coral.

The term madreporite, or fossil madrepore, was formerly applied to all the branched fossil corals with radiated cells, but is now restricted to those which possess the above characters. The recent common species, figured Wond. p. 620, will serve to illustrate this genus. The elevated, branched Madrepores, with minute polygonal cells having twelve rays, the lamellÆ of which are denticulated, are termed Porites, and are frequent in the Silurian strata (Sil. Syst.).

Millepora. Lign. 89.—Coral ramose; cells very minute, distinct, perpendicular to the surface, giving the interior a finely striated fracture, disposed irregularly.

There are many fossil species of this genus, some of which are of considerable size. A small species from the mountain limestone is figured Lign. 89, fig. 7.[248]

Lithodendron. Lign. 70, fig. 3.—Polyparium branched, formed of deep, cylindrical, elongated cells, which are terminal, and radiated, with a prominent central axis.

Large masses of corals of this genus, composed of clusters of branches, are imbedded in the mountain limestone of Derbyshire, Yorkshire, &c.; and a few species occur in the Coralline Oolite; their general configuration will be understood by the figure Lign. 70, fig. 3; but in this specimen the margins of the cells are worn off, and do not present the original deeply excavated form.[249]

There is a remarkable specimen of this coral in the Bristol Institution (of which a portion is now placed in the Museum of Practical Geology, in London), that was discovered by Mr. Samuel Stutchbury,[250] in a vein of hematitic iron ore. It is a large mass, in which the entire substance of the coral is transmuted into a metallic ore, forming one of the most interesting natural electrotypes I have ever seen. In this instance, a block of Lithodendron must have lain in a vein or fissure of the rock, and its animal membrane have resisted the action of the gaseous emanations, or mineral solutions, while the calcareous polypidom was dissolved, and the metallic matter deposited atom by atom, as in the case of pseudo-morphous crystals.

Gorgonia.—Of the flexible anthozoan coral, which from the flabellated form of the polyparium is generally called "Venus's fan," and by naturalists Gorgonia, a few fossil species have been discovered and determined. From the friable arenaceous limestone beds of Maestricht, which abound in corals, fine specimens of a delicate species are occasionally procured. Wond. p. 320, fig. 5, shows the character of this fossil zoophyte.

Fossil Bryozoa.

The second class of Polypifera, the Bryozoa or Polyzoa, are of a much higher order of organization than those which have engaged our attention. The body is not symmetrical, nor capable of contraction and expansion, as in the Anthozoa: it consists of a digestive cavity or sac, which is bent on itself and open at both extremities. The outer integument is either membranaceous or horny; sometimes calcareous. The oral aperture or mouth is surrounded by a circle of tentacula, from eight to twelve or more in number, and these tentacles are clothed with vibratile cilia. (Wond. p. 606, the polype of Flustra pilosa.)

The polypes in this order never occur singly; they are always united by a common integument, but each enjoys an individual existence. The animal can extend its tentacula and protrude the mouth from the cell, but the rest of the body is incapable of extension or contraction. These polypifera increase by germination. In their organization, they so closely approach the mollusca, that in recent zoological systems they are placed in that class. The ciliated character of their tentacula has also led to their being named Cilio-branchiata. But as it is desirable in a work of this elementary nature to avoid conflicting opinions as much as possible, the fossil Bryozoa will be considered as corals, in the general sense of that term.

Flustra (Sea-mat). Lign. 89, fig. 4, 5.—The polyparium is either membranaceous and flexible, calcareous and encrusting, or foliaceous, composed of cells, arranged in juxtaposition, more or less quadrangular, flat, with a distinct border, disposed on a flat surface, or on opposite surfaces, as in the F. foliacea.

This is one of the most common genera of the encrusting and frondescent zoophytes. The Flustra consists of a cluster, or aggregation of polypes, invisible to the naked eye; under the microscope, the polype is found to be a transparent gelatinous body bent on itself, with a sac or digestive cavity, having two apertures, the external margin of which terminates in eight or ten tentacula, clothed with cilia; the whole is surrounded by a firm wall, constituting a cell, from which the animal can protrude its tentacula and upper part. (Figures of the living polypes of FlustrÆ, Wond. p. 605, pl. vi. fig. 6, 7.)

Many species of FlustrÆ occur in the British strata: the encrusting forms are attached to echinites, shells, &c.; the foliaceous are imbedded in chalk, sand, sandstone, &c. In Mr. Morris's Cat. Brit. Foss. ten species are enumerated; none of these are from formations below the Chalk. I have selected for illustration a Flustra attached to an echinite from Lewes. Lign. 89, fig. 5, represents a small portion of the natural size; and fig. 4, a few cells magnified, to show their form and arrangement. A foliaceous zoophyte, apparently a bryozoon, is abundant in the Sussex and Kentish chalk, and is often disposed in angular folds. It is generally of a ferruginous colour, and, from its friable texture, it is probable the original consisted of a membranous polypidom or calcareous substance; specimens sometimes extend over several square inches of the chalk. It is common in the chalk-pit at Off ham, near Lewes.[251]

Eschara.[252]—In these zoophytes the polyparium is encrusting or foliaceous, calcareous and brittle; the cells are thickened on their outer margins, and have a small, depressed, round aperture. They are arranged in two series of planes, adhering together, the cells on each surface exactly corresponding.

Species of EscharÆ are found either in flints, or attached to echinites, and other bodies; they have the appearance of patches of flustrÆ, but with a lens may be distinguished by the symmetrical juxtaposition of the cells on the opposite sides of the polyparium.

Crisia Johnstoniana. Lign. 89, fig. 3, 10, 10^b.—The minute recent corals thus designated are allied to Flustra, but separated from that genus by the cells being disposed in a single series, and united by connecting tubes. I notice this genus to direct attention to a very curious polypidom from the Greensand of Maidstone, presented to me by Mr. Bensted. The specimen is attached to a fragment of shell. The cells, five of which are represented, fig. 10, are elliptical, with the aperture above, and towards one extremity; they are united by very slender, hollow filaments: fig. 3, two of the cells seen from above × 250 linear; fig. 10^b the same seen in profile.[253] I have named this species C. Johnstoniana, as a tribute of respect to the author of the admirable works on British Zoophytes, previously noticed.

The fragmentary relics of numerous minute and elegant corals, constitute a considerable portion of the mass of some of the white chalk strata; several genera of these zoophytes are figured in Mr. Dixon's beautiful work, and described by Mr. Lonsdale. Attached to the surface of shells, &c., and sometimes standing erect in little crannies, or hollows, of the flints, many beautiful corals may often be detected with the aid of a lens. By brushing chalk in cold water, and examining the deposit, the student will probably discover several of the species figured in Lign. 89, which we proceed to describe.

Retepora (Lace-Coral). Lign. 89, fig. 13.—A very thin calcareous polyparium, disposed like net-work in foliaceous and branching plates; cells opening either on the upper or inner side.

These are an elegant tribe of corals, of which many species occur in the Chalk formation at Maestricht, in the white-chalk of England, in the mountain limestone of Yorkshire, (Phil. York.), and in the Silurian deposits (Sil. Syst.). It may be useful to state, that in the description of the fossil retepores, the openings in the net-work are called fenestrules—the spaces between the ends, dissepiments—and those between the fenestrules, interstices. A delicate fossil retepore from the mountain limestone of Yorkshire (R. flexa), is figured Lign. 89, fig. 13.

Fenestrella.—Cells very small, indistinct externally, with small prominent openings; polyparium stony, fixed at the base, composed of branches, which inosculate by growth, and form a cup. Numerous delicate corals, formerly arranged as ReteporÆ, occur in the Silurian rocks, and have been placed in this genus by Mr. Lonsdale. (Sil. Syst. p. 677.)

PetalÆpora pulchella.[254] Lign. 69, fig. 1.—This beautiful cretaceous coral is "tubular, free except at the base; framework composed of vertical laminÆ, with an intermediate foraminated structure; apertures to the tubular cavities distributed over the surface; exterior varying with age." It has slender round dichotomous branches, and the polyparium when entire must have formed an elegant plexus of coral. A layer an inch thick, full of branches of this zoophyte, is exposed on the face of the chalk cliffs, near Dover; and beautiful masses, several inches square, made up of this coral, Idmonea and Pustulopora, may be obtained. The microscopic specimen figured in Lign. 69, was obtained with many other corals by washing chalk with a brush, and examining the detritus deposited.

Pustulopora. Lign. 89, fig. 8.—Another very common tubular branched coral of the Dover chalk; the tubes are cylindrical, their apertures are arranged in annular or spiral rows, and slightly projecting, giving a pustulous appearance to the stem and branches. Specimens covering a piece of chalk six or eight inches wide, and a foot long, have been discovered. The example figured is a very minute branch.

Homoesolen ramulosus.[255] Lign. 89, figs. 9, 11.—This delicate branched coral is formed of large and small tubes variously intermingled, both inclined in the same direction, partially visible on the surface, or wholly concealed, limited to one side of the coral; mouths simple tubular extremities; back without pores, composed of a continuous lamina.[256]

The elegant coral, fig. 11, Lign. 89, is thus named by Mr. Lonsdale; it resembles his fig. 4. The fossil, fig. 9, Lign. 89, though very different in its branching, and in the surface, which is covered with pores, is evidently identical with fig. 3 of Mr. Lonsdale, which he refers to the same species.

Idmonea, Lign. 89, fig. 6.—In this elegant coral the polyparium is calcareous, branched, porous; the cells distinct, prominent, arranged in single rows, more or less inclined, on each side a median line on the inner face only. The genus is extinct.

A beautiful species of Idmonea, of which a small branch is figured in Lign. 89, abounds in the chalk of Kent and Sussex; it often forms a cluster, two or three inches in circumference. The surface of the stems is covered with minute pores, and the cells are distinct, and placed in single rows; the left-hand figure of fig. 6 shows the plain surface, and that on the right, the opposite and inner, each margin of which is garnished with a row of cells; a portion magnified is represented fig. 12.[257]

Idmonea Comptoniana,[258] Lign. 89, fig. 14.—This is a very small and remarkable coral; it is dichotomous, cylindrical, with elongated distinct cells, which are disposed in triplets, at regular distinct intervals, on one side of the stem.

We have now described all the fossil corals figured in Lign. 89; and have shown what interesting organisms may be detected in a few grains of calcareous earth. It would be easy to give restored figures of the beings whose stony skeletons are the subject of these remarks, from their close resemblance to existing species; every pore and cell might be represented fraught with life; here the agile inmates, with their little arms fully expanded, and in rapid motion; there retreating within their recesses, and devouring the infinitesimal living atoms that constitute their food; or rapidly shrinking up their tentacula upon the approach of danger; even their varied colours might be introduced, and thus the beautiful and highly interesting picture drawn by the imagination, of a group of living zoophytes of the ancient chalk ocean, be presented to the eye.

Although, for convenience, I have selected the above examples principally from the cretaceous strata, the reader must not suppose that other deposits are not equally prolific in these remains. The Coral-rag of the Oolite, many beds of the Mountain limestone, and those of Dudley and Wenlock of the Silurian System, contain myriads of minute polypidoms associated with the coralline masses of which we have already treated. Exquisite figures of the Silurian corals, by Mr. Scharf, are given in Sil. Syst. pl. xv. xvi. and described by Mr. Lonsdale. A slab of the Dudley limestone often has the entire surface studded with minute corals of many species and genera, lying in bold relief, and in an admirable state of preservation.

Verticillipora (Lign. 70, fig. 4. Lign. 72, fig. 3).—Cells poriform, arranged in meshes on the surface of convex imbricating plates round a hollow axis, forming a fixed, irregular, subcylindrical polyparium. Lign. 70, fig. 4, represents a coral often met with in the gravel-pits at Faringdon, (ante, p. 228.,) which is referred by Mr, Morris to this genus. It is composed of short cylindrical anastomosing tubular branches, emanating from an expanded base, divided internally by transverse parallel plates, covered with exceedingly minute pores or cells, disposed in meshes; the plates surround a hollow axis; the structure is well shown in the figure.

Lunulites. Lign. 70.—The polyparium is stony, orbicular, convex above, concave below; concavity radiated; convexity covered with cells, arranged in concentric circles on diverging striÆ.

A species of this coral is often found in the chalk: Lign. 70, fig. 1, represents a specimen from the South Downs, discovered by Mr. Walter Mantell. The natural affinities of this genus are not determined with precision; but I have placed it with the Bryozoa in accordance with the opinion of M. de Blainville. It is an elegant white coral, and easily recognized among the minute organisms of the chalk.

Geological Distribution of Fossil Zoophytes.—Although the geological distribution of fossil zoophytes affords less striking phenomena than that of the vegetable kingdom, yet some interesting reflections are suggested by the facts we have thus cursorily noticed. We find that in the most ancient seas of which any vestiges of their inhabitants remain, these forms of vitality existed, and produced the same physical results as at the present time; giving rise to coral-reefs, and banks of coral-limestones, and largely contributing to the solid materials of the crust of the globe. Nearly 400 British species are enumerated by Mr. Morris, and the list has subsequently been greatly extended by the labours of Phillips, Portlock, Lonsdale, McCoy, Milne Edwards, and other eminent naturalists.

The Tertiary formations afford numerous species of CaryophylliÆ, FlustrÆ, EscharÆ, Spongia, &c.; and the Crag, several genera that are as yet but imperfectly determined. The older Tertiary, or Eocene deposits, contain TurbinoliÆ, AstreÆ, FungiÆ, MeandrinÆ, and species of other genera, the recent types of which are inhabitants of tropical seas.

The zoophytes of the British Chalk have been illustrated in detail by Mr. Lonsdale in Dixon's Cretaceous and Tertiary Fossils of the South-East of England; and by Dr. Milne Edwards in the Monographs of the PalÆontological Society.

In the Maestricht deposits, lamelliferous corals, as AstreÆ, FungiÆ, MeandrinÆ, &c. prevail, and may be extracted from the friable arenaceous limestones in a fine state of preservation. In the White Chalk and Greensand of this country, the Spongites and allied genera are abundant, and associated with CaryophylliÆ, AstreÆ, and many forms of Bryozoa.

But in the cretaceous formation of England, no coral-reefs are observable; the zoophytal remains, with but a few local exceptions, occur promiscuously intermingled with the fishes, shells, Radiaria, and other marine exuviÆ; although many layers, or thin seams of chalk and marl, are largely composed of the detritus of corals, like the modern deposits of the Bermudas (Wond. p. 613). These phenomena are in accordance with the lithological characters of the White Chalk strata, and the nature of its mollusca, both of which indicate a deep sea; and coral-reefs are only formed at moderate depths. But in regions where the sea was shallow, during the deposition of the cretaceous rocks, beds of coral limestone were produced; and these also contain littoral (sea-shore) shells, associated with the usual sponges and zoophytes (Wond. p. 613).

In the marine secondary formations antecedent to the cretaceous, namely, the Lias and Oolite, coral-reefs, which appear to have undergone no change save that of elevation from the bottom of the sea, and the consolidation of their materials by mineral infiltrations, demonstrate a condition of the ocean in our latitudes, which is now only met with in the tropics (Wond. p. 614).

The limestones of the Carboniferous, Devonian, and Silurian formations, abound in anthozoan corals, and among them are many kinds of Cyathophyllum, Lithododendra, Syringopora, Catenipora, Graptolites, &c., which are characteristic of these deposits.

The Silurian zoophytes are figured in Sil. Syst.; and the splendid works on the British PalÆozoic Fossils, by Prof. Sedgwick and Prof. McCoy, now in course of publication, contain many admirable figures of new, or but imperfectly known species.

The extensive beds of coralline limestones, which are found in the Silurian strata, wherever they occur,—for the limestones of this system in North America are characterized by the same species of corals as those of England,—seem to indicate that a more equal temperature prevailed throughout the ocean, at that geological epoch, than at the present time, when the geographical distribution of the coral zoophytes is strictly limited by temperature. The reef-forming genera are now confined to waters where the temperature is not below 70°; their most prolific development being 76°. The apparent exception, the occurrence of coral-reefs at the Bermudas, is found to depend upon proximity to the Gulf Stream (Wond. p. 614), which brings down the thermal waters of the tropics, and increases the local temperature of the sea in those localities.[259]

On Collecting Fossil Corals.—Few instructions are required for the collection of fossil zoophytes; for as the most important characters of the several kinds have been pointed out in the previous descriptions, the student will be able to select illustrative specimens for his cabinet. The minute corals, &c. of the Chalk, and other limestones, are to be obtained by the same process as that directed for the discovery and preservation of the foraminifera, and other microscopic organisms, at the end of the next chapter. The larger examples should be left attached to a piece of chalk, when practicable, and the surrounding stone removed with a knife or graver, so as to expose as much of the fossil as may be required for the display of its characters, without loosening its attachment to the block. When the investing chalk is very hard, frequently pencilling the specimen with vinegar, or dilute hydrochloric acid, will soften the stone, and render its removal easy, by means of a soft brush: when acid is employed, the specimen must afterwards be well rinsed in cold water.[260]

[260] It may be well to caution the collector against employing sulphuric acid (commonly called oil of vitriol) for this purpose, for a white insoluble deposit (sulphate of lime) will thus be formed on the specimen, and its appearance irremediably injured. Many of the fossil corals obtained from the chalk of Dover Cliffs, are so saturated with muriate of soda, from long exposure to the spray of the sea, as to be liable to decomposition in the course of a few weeks, and are therefore not worth purchasing of the dealers.

The zoophytes that are in part flint, and part chalk, as the Ventriculites, (ante, p. 244, Lign. 81,) can rarely be obtained, except through the quarrymen who have been instructed how to extract them from the rock. The first specimen of this kind that came under my notice, I discovered while breaking a mass of chalk, in search of fungiform flints; when, to my great delight, I found the fossil, Lign. 81, fig. 3, by which at once, and for the first time, was shown the connexion between the chalk specimens, Lign. 8, figs. 1, 2, and the flints figured in Lign. 8, figs. 2, 3, 6, 7, 8. Upon showing this fossil to the quarrymen, and exciting their attention by suitable rewards, I obtained the illustrative series now in the British Museum.[261] Much light would be thrown on the nature of other zoophytes of the chalk that are invested with flint, if due care were taken in the collection of specimens, and they were examined before extracted from the rock. Loose, delicate specimens, whether from the chalk or tertiary strata, should be affixed with strong gum-water to cards, or pieces of thin board, covered with coloured paper.

The Greensand Spongites, SiphoniÆ, &c. may often be extracted from the rock tolerably perfect, by a well-directed blow of the hammer; but fragile species should be left attached to a block, and the surrounding stone be carefully chiselled away, so as to expose the most essential characters.

The Faringdon zoophytes are, for the most part, encrusted by an aggregation of minute polyparia, shells, and detritus, which may be partially removed by washing with a stiff brush, and their cavities cleared with a stout penknife, removing the extraneous matter by chipping, not by scraping, or the surface will be injured. In this manner the beautiful specimens figured, ante, p. 228., were developed.

The Corals in the hard limestones can seldom be chiselled out to advantage; for the most part, polished sections best exhibit the form and structure of the originals.

Weather-worn or water-worn masses of coral limestone often display the structure of the zoophytes of which they are in a great measure composed, in a beautiful state of sculpture and relief: the silicified or calcified corals appearing as perfect as if fresh from the sea. The mural rocks of coral limestone at Florence Court, the seat of the Earl of Enniskillen, are in many parts encrusted, as it were, with syringopora and other tubular corals, laid bare uninjured by the long and insensible effect of atmospheric erosion. A beautiful illustration of the old aphorism,—"Aqua cavat lapidem non vi sed sÆpe cadendo,"—is afforded by the splendid examples of cateniporÆ, fungiÆ, caryophillÆ, sculptured in alto-relievo on the face of the Silurian rocks over which dash the rapids at the Falls of the Ohio.

The silicified zoophytes of the West Indies, and those from Ava and the Sub-Himalayas, form beautiful subjects for the microscope; and chips, or sections, should be prepared in the manner recommended for fossil wood in the same state of mineralization.

British localities.—The gravels and sands of the Crag afford most favourable sites for obtaining tertiary zoophytes.

In the London clay at Bracklesham Bay, a species of Astrea (A. Websteri) is often met with attached to flints and pebbles.

In the Greensand of Atherfield, in the Isle of Wight, an elegant coral (Astrea elegans) is by no means rare.

The Greensand gravel-pits, near Faringdon, in Berkshire, abound, as already mentioned, (ante, p. 228.,) in many kinds of sponges, and other porifera; and the quarries of oolitic limestone in the vicinity of that town, yield the usual corals of the Jurassic formation in great profusion, I know of no locality richer in fossil zoophytes, than Faringdon.[262]

The quarries of that division of the Oolite called Coral-rag (as in the north-west of Berkshire, Oxfordshire, Gloucestershire, &c.), afford the usual corals of the Oolite.

The Oolite near Bath contains many species, and large masses of a minute coral (Eunomia radiata), are abundant.

At Steeple Ashton, in Wiltshire, numerous oolitic corals may be obtained. The silicified AstreÆ, of Tisbury, in the same county, deserve particular notice (ante, p. 263).

Clifton, near Bristol, and Torquay and Babbicombe, on the Devonshire coast, are celebrated for their coralline marbles and pebbles; and many of the Derbyshire limestones are equally prolific in similar remains. The Devonian marbles are so largely employed for ornamental purposes,— as brooches, tables, and side-boards,—that the figures produced by the sections of the enclosed corals must be familiar to the reader.[263]

Dudley, Wenlock, and Ludlow, are well known for the abundance and variety of Silurian polyparia.

Other localities of British corals have been mentioned in the course of this review of fossil zoophytes.