Gideon Algernon Mantell

FOSSIL ARTICULATA; COMPRISING THE ANNELIDES, CIRRIPEDES, CRUSTACEANS, AND INSECTS.

The division of the Animal Kingdom termed Articulata, embraces, as the name implies, those animals which have a jointed body, generally possessing an external-jointed skeleton, composed of segments more or less annular and distinct. It comprehends six classes; namely—

1.	Annelata, or Annelida; i. e. formed of rings; comprising the Red-blooded Worms.
2.	Myriapoda; as the Centipede.
3.	Cirripedia; i. e. having curled-feet; as the Balanus and Lepas (Barnacle).
4.	Crustacea; as the Crab, Lobster, and Water Flea.
5.	Arachnida; Mites, Scorpions, and Spiders.
6.	Insecta, or Insects.

Of the first, third, fourth, and sixth of these classes, remains occur in the British strata, some being referable to existing, but the greater part to extinct species and genera. I propose to describe a few illustrative examples of the fossils belonging to each Class.Annelida.—This name is given to a class of Articulata, consisting of worms, whose bodies are formed of little rings, or annular segments, and which have red blood; as the Leech, Earth-worm, &c. Some are naked (the Dorsibranchiata and Abranchiata), and move with great celerity; as the Gordius, or Hair-worm, and the Nereis, so frequent on the sands of the sea-shore. Others have shelly coverings (the TubicolÆ), as the Serpula, and are sedentary, or fixed to other bodies. The soft bodies of certain species are protected by a coat, or tube, formed by the agglutination of sand, or other foreign substances, as in the Sabella (Lign. 123, fig. 6, p. 385).

The fossil remains of the testaceous Annelides are very abundant in some deposits; and even the naked, flexible, soft-bodied forms have left proofs of their existence in some of the most ancient sedimentary rocks. Traces of nine species, belonging to five genera of these soft, naked Annelides, have been observed in the Silurian strata of Britain.

Lign. 166. Fossil impression of Nereis. Silurian strata.
(Drawn by Miss Murray.)
Nereites Cambrensis. (Murch. Sil. Syst.) Llampeter.

FOSSIL NEREIS. SERPULA. CIRRIPEDIA.

The first notice of these remarkable remains appeared in the invaluable work of Sir R. I. Murchison on the Silurian System.[430] The living species of Nereis (Dorsibranchiate) are free, agile animals, having a distinct head, provided with either eyes or antennÆ, or both; they are the most perfect in structure of all the Annelides. The fossil represented in Lign. 166 indicates that the body of the original was composed of about one hundred and twenty segments; the feet were half the length of a segment of the body; and the cirri of the feet were longer than such segment. A more slender species, (Nereites Sedgwickii,) the body consisting of a greater number of segments, is also figured and described by Sir It. I. Murchison. Other impressions in the same stone resemble those that would be produced by smooth Annelides (Abranchiate) related to the Gordius, or Hair-worm.[431]

[430] Murch. Sil. Syst. p. 699.[431] Murch. Sil. Syst. p. 701, pl. xxvii.; and M’Coy, Cambridge Pal. Foss. p. 128, pl. 1. D.

Serpula.—The animals of this genus are sedentary or fixed, having calcareous tubes or shells, but to which they have no muscular attachment. They have plumose or arborescent gills affixed to the anterior part of the body. The shelly tubes of the SerpulÆ are constantly seen on our coasts, encrusting stones, rocks, shells, sea-weeds, &c., and may be known by their contorted or twisted forms. There are a hundred and fifty British fossil TubicolÆ. A large species has been discovered in the Silurian rocks (Murch. Sil. Syst. pl. v. fig. 1); several occur in the Carboniferous, Oolitic, and Cretaceous, and many in the Tertiary strata. In the Upper Chalk, a smooth tortuous Serpula is not uncommon (S. plexus, Min. Conch, tab. 598); it occurs in masses several inches long. But I have not observed either in the Chalk, or in any other deposit, indications of banks of SerpulidÆ, like those now in progress off the Bermudas, and which resemble coral-reefs in their solidity and extent.Cirripedia.—These animals have a soft body, enveloped in a membrane, which in some genera is protected only by a horny sheath, but in general is enclosed in a shell composed of various calcareous plates.[432] They have six pairs of feet, terminating in long, slender, articulated tentacula, furnished with cilia, and coiled up like tendrils at the extremities near the mouth. The name of the class (curled-feet) has originated from the appearance presented by the curled tentacula when projecting from the oval aperture of the shell. The testaceous Cirripedes or Barnacles are divided into two groups; namely, the sessile, or those which in their adult state are fixed by the base to other bodies, (BalanidÆ,) as the Acorn-shell, or Balanus; and the pedunculated, which have a process of attachment, peduncle or stem, (LepadidÆ,) as the Duck-barnacle, or Lepas. But the young animals of these genera have powerful locomotive organs, and are capable of swimming, by sudden jerks, like some of the crustaceans, to which class, especially in this stage of their existence, they closely approach. But after a short period of freedom, the young Cirripede fixes itself in some locality suitable to its economy, and rapidly undergoes the transformation which results in the sessile adult Barnacle or Lepas.[433]

[432] Until within the last few years the valves of the Cirripedes have been generally figured and described in works on Conchology as being allied to the Mollusca.[433] See Mr. C. Darwin’s admirable Monograph on the Cirripedia, published by the Ray Society, 1851.

Balanus. Lign. 167, fig. 1.—The shell of this sessile Cirripede is of a conical shape and cellular structure. It consists of a thick plate at the base, or place of attachment; of a series of plates, united by sutures, arranged around the body of the animal, and called parietal valves; and of pieces termed opercular valves, by which the aperture is closed. The shell of the Balanus, so common on the rocks of our shores, and on every pile and pier within reach of the tide, is composed of six parietal, and four opercular valves. The fossil Balanus, Lign. 167. fig. 1, is from the Crag, a formation containing many shells of this genus: in this example, the six parietal plates of the conical shell only remain, but in some specimens the opercular valves are also preserved. There are about twelve species of Balanus in the Crag; but none have been found either in the older Tertiary, or in the secondary rocks of England. In the newer Pliocene deposits of the Sub-Apennines, and of North America, several species are common.

Lign. 167. Fossil Barnacles and Pholades.

Fig.	1.—	Balanus tesselatus. (Sow. Min. Conch.) Crag. Suffolk.
	2.—	Loricula pulchella. (Mr. G. B. Sowerby, jun.) Chalk. Kent. a. The situation of the aperture of the shell.
	3.—	A valve (Tergum) of Scalpellum maximum. Chalk. Lewes.
	4.—	Another valve (Carina) of the same species.
	5.—	Pholas priscus[434]; in wood. Lower Green Sand. Sandgate. a. One of the shells seen in profile.
	6.—	Univalve Shells (NeritÆ) in hollows formed by Pholades. (Mr. Bensted.) Lower Green Sand. Maidstone. a. The Nerites lodged in the cavities. b. Fragment of wood remaining attached.

[434] Figs. 5 and 6 are referred to and described at pages 409 and 410, vol. i.

LepadidÆ.—The pedunculated Cirripedes, of which the common Duck-barnacle is a well-known example, have a strong, muscular, hollow stalk, or peduncle, which supports a multivalve shell, containing the body of the animal. In Pollicipes and Scalpellum there are small calcareous plates covering the junction of the body with the peduncle. Detached valves of several species of these two genera are met with in the Chalk, Galt, and Shanklin Sand, of Kent and Sussex; and three species have been found in the English Tertiary beds.[435] The valves of these fossil Cirripedes are most usually found in a disconnected state (Lign. 167, figs. 3 and 4); but the Tertiary Scalpellum quadratum is sometimes better preserved; and Mr. Morris has described a most beautiful group of Pollicipes (P. concinnus), attached to an Ammonite, from the Oxford Clay. Mr Wetherell, of Highgate, has also discovered, in the Upper Chalk, near Rochester, an almost perfect Cirripede, named by Mr. G. B. Sowerby, jun., Loricula pulchella (Lign. 167, fig. 2), and lately more fully described in detail by Mr. Darwin.[436]

[435] See Mr. Darwin’s Monograph of the Fossil LepadidÆ, PalÆontographical Society, 1851.[436] Monograph of the Fossil LepadidÆ, p. 81, pl. v.

Crustacea.—The animals whose fossil remains we have now to consider, are characterised by their crustaceous external integument or shell, which is disposed in segments, more or less distinct, the annular portions supporting articulated limbs or appendages. They are aquatic, free, locomotive beings, and possess distinct branchiÆ, or organs fitted for aquatic respiration. The Crab and Lobster are examples of those tribes in which the external crust is calcareous, and "coloured by a pigmental substance, diffused more or less irregularly through it; and is formed upon and by a vascular organized integument, or corium, which is lined by the smooth serous membrane of the visceral cavities." (Owen.) The subdivisions of this class have relation to the forms, combinations, and proportions of the primary rings or segments of the external crust or integument, but it will not be requisite for our present purpose to enter upon this department of the subject. It may, however, be necessary to mention, that in the normal type of Crustaceans, the integument consists of twenty-one rings or segments, which form the three regions into which the body is divided; namely, the head or cephalic, the thoracic, and the abdominal; each of which is assumed to consist of seven rings, although some of these are generally anchylosed, and form but one segment; and even the three regions are occasionally more or less blended together. The cephalic portion of the crust contains the principal organs of sense, and the commencement of the digestive apparatus, and includes the masticatory appendages. The thoracic portion is formed of the rings to which the extremities serving for locomotion are attached: and, together with the cephalic, contains almost all the viscera. The consolidation of the rings or segments takes place most generally in the cephalic, and next in frequency in the thoracic; and but rarely occurs in the abdominal region. These animals possess organs of sight variously modified, and in some species highly complicated; some have smooth or simple eyes (stemmata), and others compound eyes, like those of insects, with distinct facets. In one grand division (called Edriopthalmia), the eyes are sessile and immovable; in the other (Podopthalmia), they are supported upon moveable stems or peduncles. These few remarks on the organization of the recent crustaceans are required, to make our description of the fossil remains intelligible to the general reader. As the shell, or calcareous integument, even in those species in which it is very dense and thick, is moulded upon the soft parts it envelopes, the experienced naturalist is able, from its configuration alone, to obtain certain conclusions as to the form, size, and position of the contained viscera; and, as these animals annually shed their solid case and acquire a new one, which is moulded on the soft parts, the form and relative situation of the internal organs must necessarily be faithfully represented by the external integument, even when it has acquired its greatest degree of consolidation; thus the regions of the stomach, heart, branchiÆ or respiratory organs, &c. may be distinctly traced on the external shell. Hence the fossil carapaces may afford important data regarding the structure and economy of the extinct species. M. Desmarest[437] was the first naturalist who successfully applied this phrenological method to the investigation of the fossil crustaceans.

[437] Histoire Naturelle des CrustacÉs Fossiles; par MM. Alex. Brongniart et Desmarest. 1 tom. 4to. Paris, 1822.

The fossil remains of Crustaceans consist of the calcareous covering or carapace, with the articulated extremities, and, rarely, the jaws and antennÆ. For the most part, the specimens are mutilated, and present only portions of the carapace, abdominal segments, and detached claws; but in strata composed of very fine detritus, such as the cream-coloured limestones of Solenhofen and Pappenheim, examples often occur in the most beautiful state of preservation, appearing as if the animals had been carefully embalmed in a soft paste, that had quickly consolidated around them, and preserved them without mutilation or blemish. In some examples, even the colour of the original remains. The specimens found in hard limestones and coarse conglomerates are generally mutilated, and, as the under surface of the carapace, and the sternal plates to which the legs are attached, present more irregularity than the dorsal portion of the shell, they are firmly impacted in the stone, so as to render the development of some of the most important characters difficult, if not impossible. The antennÆ and claws are often separated, or altogether wanting; the most common relics being the pincers and the carapace, or united cephalo-thoracic segments. The substance of the shell, which in the recent state consists of phosphate and carbonate of lime, with gelatine or cartilage, is commonly a friable carbonate of lime, tinged with oxide of iron. These remarks apply more particularly to the crabs, lobsters, shrimps, prawns, &c. Numerous species of the smaller crustaceans, as the Cypris, and the extinct family of Trilobites, occur in myriads, and, in some formations, are the principal constituent of deposits of great thickness and extent.

The remains of this class have been found throughout the vast series of the fossiliferous strata. Extinct forms appear in prodigious numbers in the most ancient formations, and are succeeded by genera which approach more nearly to the more highly organized crustaceans. The Crab and Lobster tribes are represented by certain species in the Lias, Oolite, and Chalk; while in many of the Tertiary strata the existing types prevail.

The London Clay, in the Isle of Sheppey, yields many beautiful examples of the higher order of crustaceans, as the Crab, Lobster, &c. In the Chalk these remains are more rare, but a few fine specimens have been obtained. On the Continent, certain localities are extremely rich in these remains. Upwards of sixty species were discovered by Count MÜnster in the Jura limestone, at Solenhofen; and the Muschelkalk of Germany has yielded several extinct genera. The beautiful state in which these fossils occur, is exemplified in the specimen from Solenhofen, figured in the frontispiece of this work; Pl. I. fig. 2.

Fossil Crabs.—Of the brachyurous, or short-tailed, crustaceans, of which the common Crab is an example, and of the Anomura (abnormal-tailed), there are remains of several genera in the Tertiary deposits. The Isle of Sheppey is the most productive locality in England. The carapaces of several kinds occur in the septaria and nodules of indurated clay; the chelate hand-claws (pincer-claws) are often found detached, and sometimes in connexion with the shield. The most numerous specimens are referable to two species. One of them (Cancer Leachii) is from two to three inches wide, and has a convex shell, the surface of which is covered by minute punctations, with three tubercles on each anterior lateral margin.[438] The carapace of the other species is more distinctly lobed, and studded with aculeated or spiny tubercles; it is named C. tuberculatus.[439]

[438] Hist. Nat. Crust. Foss. pl. viii. figs. 5 and 6.[439] KÖnig, Icones Foss. Sect. fig. 54. These two species are now referred to the genus Zanthopsis.

A species of Crab, characterised by its relatively large claws, is common in the soft Tertiary limestone of Malta; and examples, in a fine state of preservation, are often seen in cabinets; see Wond. p. 251.

I am not aware that vestiges of more than one genus of brachyurous crustaceans have been observed in the British Secondary formations; namely, the Podopilumnus Fittoni (M‘Coy), from the Greensand of Lyme Regis: but several small species belonging to the anomurous group have been found in the Galt.

In the Galt at Ringmer, a village near Lewes, I discovered, many years since, four or five species of small crustaceans, which are figured and described, Foss. South D. pl. xxiv.; their natural relations were pointed out to me by the late eminent naturalist, Dr. Leach. Specimens of two of the species have since been collected at Folkstone, but as these are only the carapaces, no additional light has been thrown upon the structure of the originals.

The smallest species consists of the carapace or cephalo-thoracic segments, united into a transversely obovate, obscurely trilobate shell, the surface of which is covered with minute irregular papillÆ; with four tubercles on each lateral portion, and an irregularly tuberculated dorsal ridge (see Lign. 168, fig. 1, 1a.); it probably belongs to the genus Etyus; and I have named it Etyus Martini, in honour of my friend, P. J. Martin, Esq., author of several excellent Memoirs on the Geology of Western Sussex.

Lign. 168. Fossil Crustaceans: nat. Galt. Near Lewes.]

Fig.	1.—	Etyus Martini (G. A. M.): showing the empty carapace or shell. Ringmer.
	1a.—	The dorsal surface of the same.
	2.—	Corystes[440] Stokesii (G. A. M.). Ringmer.
	3.—	Corystes[440] Broderipii (G. A. M.). Ringmer.
	3a.—	The under surface of the same species, displaying the sternal plates and the bases of the claws, three of which are marked a, a, a.

[440] These two crustaceans are included in the fossil genus Notopocorystes, established by Professor M’Coy, 1849.

There are two species that appear to have some relations with Corystes, a genus which includes several recent crustaceans that inhabit our shores, and are characterised by their elongated oval shell and four antennÆ, the external pair being long, setaceous, and furnished with two rows of cilia. The tail is folded under the body when the animal is in repose. They have ten legs, the anterior pair chelate (with pincers), the others terminating in an acute elongated nail or claw. The fossils consist of the carapace, and one example possesses the inferior or thoracic plates and the remains of the bases of some of the legs (see Lign. 168, fig. 3a).

Notopocorystes Stokesii. Lign. 168, fig. 2.—The carapace is relatively wider than in most species of this genus; is has a strong dorsal ridge of irregular oblong tubercles; the union of the cephalic and thoracic segments is marked by a transverse undulated groove; there are three or four tubercles on the surface of each lateral portion of the former, and one on each of the latter. The whole surface is finely granulated. The openings left by the attachment of the peduncles of the eye remain.

Notopocorystes Broderipii. Lign. 168, fig. 3.—This species, like the former, has a transverse undulated furrow, indicating the union of the cephalic with the thoracic segments; the dorsal ridge is smooth, and there are two tubercles on each lateral cephalic portion of the shield. The carapace is longitudinally ovate, much depressed, with three sharp points directed forwards on each margin of the anterior part: the whole surface is finely granulated. In the specimen fig. 3a the sternal plates, with portions of the first joints of the claws, remain; one example (figured Geol. S. E. p. 169) possessed six or seven arcuate abdominal segments, which were turned under the body.[441]

[441] I have described these small crustaceans somewhat minutely, and have given them specific names, in the hope of directing the attention of collectors to these highly interesting relics, and leading to the discovery of more illustrative examples. See Foss. South D. pp. 96, 97.

The carapace or shell of the other crustacean observed in the Sussex Galt (Notopocorystes Bechei) is of an orbicular inflated form (see Geol. S. E. p. 169, fig. 3), and ornamented with twelve or thirteen aculeated tubercles; its margin is dentated.

In the friable arenaceous limestone of the Cretaceous formation at St. Peter’s Mountain, near Maestricht, the cheliferous claws of a small kind of crustacean (Mesostylus Faujasii, Wond. p. 338), are frequently discovered (and occasionally in the Chalk of Kent and Sussex), but with no vestige of the carapace or shell. This curious fact is explained by the analogy existing between the fossil claws and those of the Pagurus, or Hermit-crab, whose body is only covered by a delicate membrane, the claws alone having a calcareous covering; hence the latter might be preserved in a fossil state, while no traces of the soft parts remained. In the fossil, as in the recent claws, the right arm is the strongest. There is no doubt that the crustaceans to which the fossil claws belonged possessed the same modification of structure as the recent (anomurous) Hermit-crab, and must have sought shelter in the shells of the mollusks with which their durable remains are associated.

FOSSIL LOBSTERS.

Fossil Lobsters.—The macrurous, or long-tailed, crustaceans, as the Lobster, are distinguished from those of the former divisions by the prolonged abdomen (or tail, as it is commonly termed), which forms a powerful instrument of locomotion, and enables the animal to dart backwards through the water with great rapidity; and this is furnished with an appendage or tail, which none of the ambulatory crustaceans possess.

Of the fresh-water species, the Cray-fish (Astacus fluviatilis), and of the marine, the Lobster (Astacus marinus), are illustrative examples. The remains of three macrurous species occur in the London Clay of the Isle of Sheppey, associated with congenerous crustaceans; and the segments of the tails (post-abdomen) are often well preserved.

The Chalk contains a few species of the Macrura, which were first discovered in the quarries near Lewes, and are figured in Foss. South D. tab. xxx. xxxi.; they are among the most rare and delicate of the fossils of the Cretaceous strata. These remains consist of the carapace and claws, and rarely of the tail and antennÆ, and are composed of a friable earthy crust, which, when first discovered, is of a dark chocolate colour, but quickly changes to a pale fawn, or reddish brown, by exposure to the air. In the specimens obtained by breaking the stone, the crustaceous covering remains attached by its rough external surface to one portion of chalk, and on the corresponding piece are sharp casts of the carapace and claws, having a glossy surface covered with minute papillÆ formed by the bases of tubercles or spines. Four species have been observed.

Enoploclytia Leachii. Lign. 169, figs. 1, 2, 3.—This is a long delicate crustacean, having a pair of equal, slender, anterior chelate claws, the fingers of which are long, attenuated, and armed with a row of obtuse cylindrical spines. The surface of the hand-claws is muricated, or covered with short erect aculeated tubercles. The pincers in the specimen figured Lign. 169, fig. 3, are shorter than in most examples. The carapace is elongated and sub-cylindrical, with a dorsal ridge and two lateral furrows, indicating the normal division of the cephalic and thoracic segments of the shield; the antennÆ are long, filiform, and setaceous (bristly), and are placed on squamous peduncles (see Lign. 169, fig. 2).

There appear to have been five legs on each side; the anterior or chelate pair are the most usual relics of this animal; of the other claws and the branchiÆ, but obscure indications have been obtained. The abdominal segments are arcuate, and six or seven in number; their surface is granulated; the appendage, or tail, is foliaceous and marginate, with a few longitudinal ridges (see Lign. 169, fig. 1).[442] The claws of these crustaceans may be easily recognised by their general aspect, and the length and straightness of the fingers or pincers. In most examples traces remain of the tendinous expansion of the muscles of the moveable claw (see Lign. 169, fig. 3).

[442] See Foss. South D. p. 221, et seq. for further details.

Lign. 169. Fossil Crustaceans: nat. Chalk. Lewes.

Fig.	1.—	Abdominal appendage, or tail, of Astacus[443] Leachii (G. A. M.), with three abdominal segments.
	2.—	Part of the head of Astacus Leachii, with remains of the squamous peduncles of the antennÆ, and of the long setaceous antennÆ.
	3.—	Chelate claw, with part of the carpus, or wrist, of Astacus Leachii.
	4.—	Chelate claw of Astacus[443] Sussexiensis (G. A. M.).

[443] These fossil Lobsters are now to be referred to Prof. M’Coy’s genus Enoploclytia.

Enoploclytia Sussexiensis. Lign. 169, fig. 4.—The claws of this species are readily distinguished from the former by their broader and stronger proportions, and spinous character; the pincers are strong and tuberculated, and the moveable finger is more curved and shorter than its opponent. The entire crust of this lobster is muricated, or beset with spines and sharp tubercles.[444]

[444] Foss. South D. tab. xxx. fig. 3. In the beautiful work of the late Mr. Dixon, on the Fossils of Sussex, there are figures of very fine specimens of these two species of Enoploclytia (plate xxxviii*.) with detailed descriptions by Prof. Bell (p. 344); but unfortunately, from inadvertence, no reference is made to my former drawings and descriptions of these fossil Lobsters of the Chalk, and new names are given by the Professor; E. Leachii appearing as "PalÆastacus macrodactylus," and E. Sussexiensis as "P. Dixoni." I need scarcely remind my readers that according to the established rules of Nomenclature the earlier specific names must be preserved; and that, Prof. M‘Coy having already indicated the distinction of these fossils from the recent Astacus by providing an appropriate generic appellation, these new names are altogether inadmissible.

Claws of other AstacidÆ have been found in the Chalk of Sussex and Kent; one species in particular is distinguished from those previously described by its short curved pincers, and granulated surface;[445] and remains of other species of Enoploclytia, from near Cambridge and Maidstone, are described by Prof. M’Coy.

[445] This species may be named Astacus cretosus, to indicate its geological habitat.

The "Lobster-clays" in the Lower Greensand, or Neocomian, beds at Atherfield afford numerous fine specimens of a small long-clawed crustacean, allied to Astacus; a fine specimen is figured in the Geology of the Isle of Wight, title-page vignette, and see page 232. One or more species, apparently distinct from those of Atherfield, have been discovered by Mr. Beckles in beds of clay that appear to occupy the line of junction between the Wealden and Greensand, on the Sussex coast, between Pevensey and Bexhill.

Imperfect claws of AstacidÆ have also been found at other places in the Shanklin Sand; and I have collected from the Galt at Ringmer, the abdominal segments of a small species, resembling Meyeria ornata, Lign. 170.

Lign. 170. Fossil Crustacean. Speeton Clay. Yorkshire.
Meyeria ornata: nat. (Phillips and M’Coy.)

The carapaces of two or three small AstacidÆ, sometimes with the abdominal segments attached, as in the beautiful fossil figured in Lign. 170, are found in the Speeton Clay, near Scarborough. In this example the post-abdomen and its appendages are entire, and traces remain of the antennÆ and some of the feet. These specimens are commonly imbedded in masses of indurated clay, as the fern-leaves in the Carboniferous ironstone, and are discovered by splitting the nodules through their longest diameter. The carapace of another small species (Glyphea rostrata)[446] occurs in the Oolite of Scarborough. My friend, the Rev. J. B. Reade, has also discovered an example of this species in that rich repository of organic remains, the Kimmeridge Clay, at Hartwell, Bucks.

[446] This is the Astacus rostratus of Prof. Phillips’s Geol. York. vol. i. tab. 4, fig. 20.

A remarkable macrurous crustacean (Eryon Cuvieri) is found in the Jurassic limestone of Solenhofen. Perfect specimens of this species are occasionally seen in collections; it is distinguished by its very large, flat, oval shell, with the front lateral margins strongly dentated, and by its short setaceous antennÆ; the front claws are as long as the body, and armed with pincers; the post-abdomen consists of six segments, terminating in a caudal appendage or tail.

In the United States several fossil crustaceans have been noticed in the Cretaceous strata of New Jersey; some of which are said to be related to Pagurus, and others to Astacus.

Fossil Prawns and Shrimps, of exquisite beauty, are found in the lithographic limestone of Pappenheim: a specimen from that locality (PalÆmon spinipes) is figured Wond. p. 513: see also Frontispiece of this work.

A large crustacean of the Shrimp family has been discovered by the Earl of Enniskillen in the Lias of Lyme Regis.[447] Other specimens also of Macrura, more or less perfect, have been obtained from the same rich mine of organic remains: especially some in which the branchiÆ, or respiratory organs, remain; and a portion of the post-abdomen, or tail, of a Cray-fish, as large as the common species.

[447] This beautiful fossil is figured and described by Mr. Broderip, Geol. Trans, second series, vol. v. pl. xii. under the name of Coleia antiqua.

FOSSIL ISOPODOUS CRUSTACEANS.

Isopodous Crustaceans. Lign. 171.—Isopoda (equal-feet) is the term applied to an order of crustaceans in which the body is composed of a distinct head, and seven rings, each having a pair of equal feet; the common Oniscus, or wood-louse, is a familiar example of a terrestrial Isopod. This order includes many genera and species, some of which nearly approach the extinct family of crustaceans (Trilobites) whose remains abound in the palÆozoic strata; and the parasitical Isopod, Bopyrus, that infests the common Prawn, is closely related to certain genera of Trilobites, hereafter described.

Lign. 171. ArchÆoniscus Brodiei. Purbeck limestone. Vale of Wardour. (Drawn by S. P. Woodward, Esq.)
Impressions of the upper and under surfaces.

One species of fossil Isopod has been found in green fissile marl, at Montmartre; and another in fine-grained limestone, probably, from Pappenheim.[448] No fossil remains of this order had been noticed in the British strata, until the discovery of the ArchÆoniscus in the Purbeck strata by the Rev. P. B. Brodie. The quarry in which these relics were found is situated at Dallards, near the village of Dinton, about twelve miles west of Salisbury. They are principally distributed in a bed of light-brown and grey limestone, in the lower part of which are numerous fresh-water bivalves (cyclades), and a few small oysters. These Isopods often occur in clusters (see Lign. 171); the lenses of the compound eyes are sometimes detectable in the limestone, and, rarely, attached to the head; traces of legs have been observed, but no antennÆ. In the same stratum the elytron (sheath, or wing-case) of a coleopterous insect was discovered. Mr. Brodie has obtained specimens an inch and a half in length, and an inch broad. These fossils appear to have been deposited tranquilly at the bottom of the water which they inhabited, since they are usually found imbedded with their legs downwards, and generally well preserved.[449]

[448] Nat. Hist. Crust. Foss. p. 138.[449] See Brodie’s Fossil Insects, pp. 3 and 10.

The ArchÆonisci also occur in the Purbeck insectiferous limestone of Durlstone Bay, near Swanage, and have been discovered in strata of a similar character at the Ridgway railway-cutting between Dorchester and Weymouth, by the Rev. Osmond Fisher, of Dorchester.

Entomostraca.—The Crustaceans that we have above noticed belong to the Sub-class Malacostraca; and we have now to describe some fossil genera belonging to various divisions of the Entomostracous Crustaceans.

Lign. 172. Fossil. Limulus, in a Nodule of Ironstone: ¹/₂ nat.
Carb. Coalbrook Dale.

Fig.	1.—	Limulus Rotundatus, the imprint of fig. 3.
	2.—	The nodule before it was broken.
	3.—	Limulus Rotundatus, (the corresponding portion of the nodule, fig. 1,) showing the entire form of the carapace.

FOSSIL LIMULUS.

The Limulus (Mollucca or King Crab) is a genus belonging to that Division of the Entomostraca termed Poecilopoda and is abundant in the seas of India and America. The carapace is crustaceous and of a semilunar form, the head and thorax are blended together, and the superior abdominal shield, which is composed of confluent segments, appears like one piece, and has an indistinct trilobed character; the last segment is prolonged into a three-edged, sharp, styliform weapon. The Limulus has two reniform, compound eyes, composed of facets of a peculiar form. The gills are disposed on lamelliform processes. It is distinguished from all other crustaceans by the mastication of its food being performed by the first joint of the thoracic legs which surround the mouth, instead of by jaws.

Lign. 173. Limulus trilobitoides.
Coal Measures. Coalbrook Dale.

Very fine examples of a fossil species of this remarkable genus are occasionally obtained from the lithographic stone of Solenhofen.[450] In England three small species have been discovered in nodules of ironstone and indurated clay, in the Carboniferous strata of Coalbrook Dale, by Mr. Prestwich.[451] In one example (L. Anthrax[452]) two of the legs are seen extending from under the body; in another species the sharp, pointed process of the tail is well developed (Buckl. p. 396, and tab. xlvi.; see also Lign. 173). The specimen figured Lign. 172 is one of several examples which I obtained by breaking up nodules from that celebrated locality. Fig. 2 represents the nodule unbroken, and without any indication of its contents; by a well-directed blow it was separated into two equal portions, figs. 1 and 3, in which the carapace of the crustacean, and its marginal appendages, are well displayed. The rounded form of the carapace, and the membrane which appears to connect the spines, separate this species from all others.

[450] Hist. Crust. Foss. pl. xi. fig. 6.[451] See Mr. Prestwich’s Memoir on the Geology of Coalbrook Dale, Trans. Geol. Soc. second series, vol. v. part 3.[452] Trans. Geol. Soc. second series, vol. v. pl. xli. figs. 1-4.

The Eurypterus and Pterygotus are palÆozoic crustaceans, of large size. They are regarded by Prof. M‘Coy and Mr. Salter as belonging to the Poecilopoda, and as differing from the Limulus chiefly in having the segments of the abdomen freely articulating with each other.[453] The Eurypterus was first described by Mr. Dekay, in the United States, probably from the Carboniferous system. The head is round, the thoracic and cephalic portions of the carapace being blended together, and the abdominal region is formed of eleven segments, with a caudal appendage. It has two depressed, lunated eyes, remote from each other, and eight feet, the anterior pairs furnished with branchiÆ, and the hindmost pair relatively larger than in any other crustacean. Two American species are described; the one is five, and the other about four inches long.[454] In the Carboniferous strata at Burdie-house, near Edinburgh, and of Kirton, near Glasgow, a large species of this curious genius has been found by Dr. Hibbert and Dr. Scouler; the length of some specimens being estimated at from twelve to eighteen inches.[455]

[453] See Salter on Pterygotus, Quart. Journ. Geol. Soc. vol viii p. 387.[454] Dr. Harlan, in Trans. Geol. Soc. Pennsylvania, vol. i. p. 96.[455] See the elegant Memoir on the Fresh-water Limestone of Burdie-house, near Edinburgh, by Samuel Hibbert, M.D. F.E.S.E.

Other species of Eurypterus have been noticed in the Upper Silurian rocks of Kendal, Westmoreland,[456] and of Kington, Radnorshire; and in the Devonian of Russia.

[456] Pal. Foss. Cambridge, Appendix.

Pterygotus.—In the Old Red sandstone of Forfarshire, and other parts of Scotland, the remains of this remarkable crustacean have been long known to the quarry-men by the name of "petrified Seraphims;" from an imaginary resemblance of the expanded post-abdomen to the usual representations of those ideal beings! This genus is characterised by the angular carapace, which forms a lozenge-shaped shield; and the appendage of the post-abdomen, which, instead of being divided into segments, as in most animals of this class, is a continuous flap. The eye-pits on the carapace are like those of Eurypterus, but are very large. The claws resemble those of the common lobster. The external crustaceous covering is ornamented with circular and elliptical markings, producing an imbricated or scaly appearance, the imprints of which gave rise to the enigmatical "Seraphims" of the Forfarshire sandstone. Some specimens indicate a total length of four feet![457]

[457] The Old Red Sandstone, or New Walks in an Old Field, by Hugh Miller, p. 147. There are specimens in the British Museum from the quarries of Carmylie.

Besides this Devonian species (P. anglicus), there is also a Silurian species (P. problematicus), from Herefordshire.[458]

[458] See Quart. Journ. Geol. Soc. vol. viii. p. 386.

---

Several fossil genera of the Entomostracous Crustaceans belong to the Phyllopoda (leaf-feet), which constitute a subdivision of the Branchiopoda (gill-feet). Of these perhaps the most remarkable is the Dithyrocaris, first discovered by Dr. Scouler in the Carboniferous shale near Paisley. This genus is allied to the recent Apus, and, like it, has a broad, flat, thin carapace, easily divisible down the middle of the back, and a lengthened tail or post-abdomen, with a trifid termination. Six species have been found in the Carboniferous deposits of the British Isles.

Ceratiocaris and Hymenocaris, which are related to the recent Nebalia, are also of the Phyllopod group, and maybe said to resemble a shrimp-like animal partly enclosed in a bivalve carapace, while its tail is exposed, and either protruded, or turned beneath the body. Of the first-mentioned genus there are three Upper Silurian species; and of Hymenocaris Mr. Salter has described a single species (H. vermicanda) from the Lower Silurian (Cambrian) of North Wales.

The LimnadiadÆ,—another Phyllopodous family, of which the recent Limnadia is the type,—are well represented in the older rocks. These Crustaceans are also bivalved, but the body is wholly enclosed. They are of small size. Estheria, a genus closely related to Limnadia, occurs plentifully in the Wealden of Sussex and Germany, and in the Lias of Westbury. Mr. Bean also has noticed a species (E. concentrica) in the Oolite shell of Gristhorpe Bay; and the E. minuta[459] is characteristic of the Keuper division of the Trias in England and Europe.

[459] This was formerly described as a Posidonomya.

Leperditia and Beyrichia are other fossil genera belonging to the LimnadiadÆ. These little crustaceans were gregarious in their habit, and, like Estheria, occur locally in great profusion. They are characteristic of the Silurian deposits; the former being an abundant Upper Silurian fossil in Europe and North America, and the latter,—a very minute form,—both in the Upper and Lower Silurian.

The next group of Entomostraca that we have to notice belongs to the Lophyropoda (feet crested with bristles), namely, the Ostracoda (shelled). The recent genera, Cypris, Cythere, and Cypridina,[460] are types of the three families of this group, and are the existing representatives of numerous closely related forms that occur in a fossil state.

[460] The student should consult Dr. Baird’s elegant and elaborate work on the Natural History of the British Entomostraca (published by the Ray Society), for information on the characters and habits of these interesting little crustaceans and their numerous allies

Lign. 174. Fossil Cyprides. Wealden. Sussex and Isle of Wight.

Fig.	1.—	Cypris Valdensis: magn.; showing the ventral aspect of the united valves. Cooksbridge.
	1a.—	Side view of the same, magn. The three small figures are of the nat. size.
	2.—	Cypris Fittoni, magn. Langton Green.
	3.—	Cypris tuberculata, magn. Langton Green.
	3a.—	View of the same, showing the lower edges of the valves united: the three small figures, nat.
	4.—	Cypris granulosa, magn.; view showing the hinge-line.
	5.—	A piece of Weald Clay, with Cyprides and Shells; nat.

Cypris. Lign. 174.—The animals of this genus belong to those Crustaceans in which the covering of the body is not divided into transverse segments, but consists of a large dorsal shield, having the form of a bivalve shell. They are often very minute, and numerous kinds swarm in our lakes and pools. The species of an allied genus, named Cythere, the shells of which cannot always with certainty be distinguished in a fossil state from those of Cypris, inhabit salt or brackish waters. As the living Cyprides are interesting objects for microscopic examination, they are commonly shown in the exhibitions of the hydro-oxygen microscope, and their appearance is therefore well known. Two recent species are figured in Ly. p. 183. These animals have the body enclosed in a bivalve, horny case, the two pieces being united by a hinge-line. They have four feet, and two pairs of antennÆ, with a pencil of cilia at the extremities; and one compound eye. They swim with rapidity, by means of their ciliated antennÆ, and crawl about actively on the water-weeds and other subaqueous surfaces. Like the other crustaceans, they frequently moult or cast their cases, and the surface of the mud spread over the bottoms of still lakes is often covered with their exuviÆ. The largest living Cypris (C. clavata) does not exceed one-eighth of an inch in length. The fossil cases or shells of Cyprides are found in considerable variety and in prodigious numbers in certain Tertiary and Secondary strata, which appear to have been deposited by fresh-water; as, for example, in the lacustrine marls of Auvergne (Ly. p. 183), and the fluviatile clays and limestones of the south-east of England. They have not been observed in any decidedly marine beds; but Mr. Lonsdale discovered in the Chalk, by means of the microscope, cases of crustaceans, that belong to the genus Cythere (Ly. p. 26, figs. 21-24), the recent species of which inhabit the sea. One or more species of Cypris have been observed in the older British Tertiaries,—by Sir C. Lyell, in Hordwell Cliff (Geol. Trans. 2d ser. vol. iii. p. 288), and by Mr. Prestwich at Hempstead Cliff (Brit. Assoc. 1846); but in the Pleistocene deposits the Cypris and its congeners abound, and of these Mr. R. Jones has enumerated nine species (Annals Nat. Hist. 2d ser. vol. iii.). In many districts on the Continent, the Eocene marls and clays abound in these remains. Some of the fresh-water Tertiary strata of France contain myriads of a Cypris (named C. faba, from its bean-like form) which was formerly supposed, but erroneously, to be identical with a species found in the Wealden. The laminated marls of Auvergne contain, between every layer, countless myriads of the shells of Cyprides, through a depth of several hundred feet; although each lamina of marl scarcely exceeds the thickness of paper. Near Clermont, the green cypridiferous marls approach to within a few yards of the granite which forms the borders of that ancient basin (Ly. p. 184). In the eastern portion of the basaltic districts of India, Mr. Malcolmson has discovered two species of Cypris, associated with fresh-water univalves and bivalves.[461] In England the principal deposits of the Cyprides, are the clays and limestones of the Wealden and the Isle of Purbeck,[462] to the composition of which the relics of these minute beings have largely contributed. Entire layers of their cases are found in the laminated clays and marls on the southern shores of the Isle of Wight, at Atherfield and Sandown Bay, where some of the Wealden beds emerge from beneath the lower division of the Shanklin sand. Upon splitting the clay in the direction of the laminÆ, the exposed surfaces are found to be covered with these minute bodies; as in the specimen, Lign. 174, fig. 5.

[461] Geol. Trans. 2d ser. vol. v. pl. xlvii.[462] On account of the distinctive characters of their carapace-valves, M. Bosquet has suggested the appellation Cypridea as a generic name for the CyprididÆ of the Wealden and Purbeck beds.

The appearance of four characteristic Wealden Cyprides, of their natural size and magnified, is shown in Lign. 174. The one named C. Valdensis, or Wealden Cypris, by Dr. Fitton and Mr. Sowerby (fig. 1), is the most frequent, and occurs in numerous localities in Kent and Sussex. A Cypris having the case studded with relatively large tubercles (fig. 3), is found in many of the finer sandstones of Tilgate forest; another, with the shell tuberculated, but divided by a transverse ridge (fig. 2), indicating a rudimentary condition of the segments which characterise the class, is certainly distinct from the former, and can have no name more appropriate than that of C. Fittoni. The other beautiful species (C. granulosa, fig. 4) has the surface of the case covered with granules. One more species has been observed in the Weald clay, at Sandown Bay and Atherfield (by Mr. Lonsdale); it is distinguished by a short conical spine on each valve, and is therefore named C. spinigera. In the Weald clay at Resting-oak-hill, near Cooksbridge (Geol. S. E. p. 187), C. Valdensis is so abundant, that every thin flake is covered with its white calcareous shells; and upon breaking the nodules and septaria of reddish-brown ironstone which occur in that locality, myriads of beautiful sharp casts of the cases are observable in almost every fragment. They are associated with fresh-water bivalves and univalves (Cyclas and Paludina), and minute scales of fishes. The sandstone at Langton Green, near Tunbridge Wells, which contains casts and impressions of several species of fresh-water shells, abounds in Cyprides; and the layers of argillaceous ironstone, interstratified with the sandstone in one of the quarries, are particularly rich in these remains. The surface of a recently broken slab is often covered by minute, polished, oblong, convex bodies, which are the casts of cypridean carapaces.

The Sussex marble is largely composed of the remains of these minute crustaceans. Upon examining thin polished slices of this limestone under the microscope, the cavities and interstices of the shells are found to be filled with the shields of Cyprides, entire or in fragments; and some specimens of the Purbeck marble equally abound in these remains. The Purbeck marls, as well as the limestones, often abound with Cyprides. According to Prof. E. Forbes, these belong to several species, all more or less distinct from those of the Wealden (Brit. Association, 1850). The Cyprides of the Wealden of Germany have been figured and described by Dr. Dunker; and several of the British forms are found there.

As the recent species inhabit still lakes, or gently running streams, and not the turbulent waters of estuaries, we cannot doubt that the strata in which these animals so largely predominate were deposited in lakes or bays, communicating with the river which transported to their present situation the bones and other remains of the colossal reptiles of the Wealden. And the beds of fresh-water snails, with scarcely any intermixture of other organic remains but the Cyprides, which are spread over extensive areas in the Wealden and Purbeck districts, appear to afford corroborative proof of this inference.

Four species of minute bivalved Entomostraca from the Carboniferous deposits have been referred to Cypris: viz. C. arcuata, Bean, from the Coal-shale at Newcastle; C. inflata, Murchison, Coal-measures, near Shrewsbury; C. Scoto-Burdigalensis, Hibbert, Coal-measures at Burdie-house, and Coal-shale at Derry; and C. subrecta, Portlock, also from Derry, Tyrone.

Cythere.[463]—This animal differs but little from Cypris except in having an additional pair of feet. In the Subgenus Cythereis the valves are thick, oblong, and strongly hinged; thus differing from the thin and more or less oval valves of the true Cythere and of Cypris. Several species of Cythere and its sub-genera occur in the Tertiary, Cretaceous, Oolitic, Liassic, Permian, and Carboniferous deposits.[464]

[463] For description and illustration of this genus, see Baird’s British Entomostraca, p. 163, &c.[464] Consult M. Bosquet’s Memoir on the Tertiary Entomostraca of Belgium and France; Mr. T. R. Jones’s Monograph of the Cretaceous Entomostraca (PalÆontographical Society), and of the Permian Entomostraca, in Prof. King’s Monograph of the Permian Fossils (PalÆont. Soc.); and Prof. M’Coy’s Synopsis of the Characters of the Mountain Limestone Fossils of Ireland.

Three species of Entomostraca, very closely related to Cypridina,[465] from the Carboniferous rocks of Belgium, hare been figured and described by M. De Koninck; one species from the Carboniferous rocks of Ireland, by Prof. M’Coy;[466] and two species from the Cretaceous limestone of Maestricht,[467] by M. Bosquet. The genera Cyprella and Cypridella have been established by M. De Koninck for the reception of some allied forms found in the Carboniferous strata of Belgium; and Entomoconchus (M‘Coy) and Daphnoidia (Hibbert) are allied British Carboniferous forms.

Trilobites.—Among the numerous petrifactions which are found in the limestones in the neighbourhood of Dudley, in Staffordshire, there are certain fossil bodies which, from their extraordinary form and appearance, have for more than a hundred and fifty years been objects of great interest to the naturalist, and of wonder to the general observer, and have long been provincially termed Dudley insects, or locusts.[468] By the earlier naturalists these fossils were referred to fishes, to molluscs, and to insects, before their real character was discovered. The most common type consists of a convex, oblong body, divided transversely into three principal parts, and longitudinally into three lobes, by two deep, parallel furrows; this last character suggested the name Trilobita, or Trilobites, by which the family is now distinguished by naturalists.

These fossils are the carapaces, or shells, of crustaceans, belonging to an extinct family,[469] which comprises many genera, and numerous species. Mortimer, Da Costa, Guettard, and LinnÆus recognised the crustacean character of this interesting, but obscure class of organic remains: their true affinities, however, were first scientifically determined by Alex. Brongniart.[470] Many memoirs on the Trilobites have since been published by eminent Continental and American writers;[471] and much light has been thrown on the subject by the labours of Martin,[472] Parkinson, [473] Stokes, Phillips,[474] KÖnig,[475] Dr. Buckland,[476] Sir E. I. Murchison,[477] and others. The beautiful illustrations and interesting description of the Trilobites in Dr. Buckland’s Bridgewater Treatise (Bd. p. 389, and pl. xlv. xlvi.) must have rendered the reader familiar with the most important facts relating to these extinct beings; but subsequent discoveries have thrown additional light on their structure and natural affinities. The works of M. Burmeister,[478] Mr. Salter,[479] Prof M’Coy[480] and especially of M. Barrande,[481] should be carefully referred to by the student in this branch of PalÆontology.

In the Trilobites the head is distinct, and without antennÆ, and the feet are supposed to have been rudimentary, soft, and membranaceous: the essential characters which separate them from all other crustaceans, except Bopyrus (a parasite on the branchiÆ of the common prawn), are, according to Mr. Macleay, the deficiency of antennÆ, and of lateral posterior abdominal appendages, and the presence of evanescent feet. Like other crustaceans, the Trilobites were subject to the process of metamorphosis during their early stages of life; and M. Barrande has ascertained that one species, the SaÖ hirsuta, appeal’s in no less than twenty different stages of development. In its earliest, embryonic condition, it is a simple disk, and it passes through various stages until it becomes a perfect adult trilobite, having seventeen free thoracic segments and two caudal joints. No less than ten genera and eighteen species were instituted by palÆontologists on some of the forms only which this one species presents in its different stages of metamorphosis, before M. Barrande’s laborious and long-continued investigations gave him an insight into the true relations of these various conditions of the same animal to one another. This talented and indefatigable palÆontologist has arrived at like results with other Trilobites, and has been enabled to add greatly to our knowledge of the natural history and geological distribution of this interesting group of crustaceans. See Transact, of the Sections, Brit. Assoc. 1849 and 1850; and Trilob. BohÊme, pl. vii.

The Trilobites have been arranged in numerous genera, the names of which in a few cases are expressive of natural characters, but in others have reference to the obscurity that still invests some parts of the organization of these animals.[482]

Calymene Blumenbachii. Lign. 175, figs. 3, 4.—This is the Trilobite so well known as the Dudley locust, or insect. It consists of an ovate, convex, trilobed crustaceous shell, or case, and is found either expanded, as in Lign. 175, fig. 3, with its under surface attached to, and blended with, the limestone (Wond. p. 789); or coiled up like an Oniscus, or wood-louse, as in figs. 4 and 4a. The head is large, convex, rounded in front, with a broad border, and divided into three lobes by two longitudinal depressions. The eyes are two in number, compound, and have numerous facets; they are situated on the sides of the head, remote from each other. The carapace is deeply trilobed by two longitudinal furrows; the thoracic portion is composed of thirteen segments; the caudal shield is small and nearly semicircular. This species is from one to four inches in length. It occurs from the Lower Llandeilo rocks up to the Upper Ludlow inclusive.

The structure here described may be regarded as the normal type, but numerous and important modifications prevail in the different genera.

In the genus Homalonotus, Lign. 176, the thoracic portion of the carapace is but obscurely lobed, and consists of thirteen segments; the abdominal is distinct from the thoracic, and formed of nine rings; it terminates in a prolonged point. The H. Herschelii is a large Trilobite, very plentiful in the Upper Silurian schists of the Cape of Good Hope.

In another genus, Asaphus (Geol. Surv. Decade 2), the carapace is wide and much depressed; the middle lobe distinct, the cephalic portion rounded in front, and terminating posteriorly in a sharp process on each side. The eyes are compound, and each contains upward of six thousand lenses, many of which remain in some examples.[483] Some American species belonging to this group are of a gigantic size, as, for example, the Isotelus gigas (of Mr. Dekay), which is eighteen inches long. In the Isotelus[484] the body is of an oval shape, and the posterior angles of the head are rounded; the thorax is composed of eight segments.

Another division of the Trilobites has the body contracted, and very thick, and the abdomen large and scutiform, without any segmentary divisions; the small crustacean (IllÆnus perovalis, Murch.) Lign. 175, fig. 1, will serve to illustrate these characters.

The Trilobite called Bumastus by Sir R. Murchison (from its grape-like form) presents a very curious modification of the normal type. Both the head and caudal extremity are rounded, with no distinct longitudinal furrows; and the whole surface of the carapace is covered by extremely thin, apparently imbricated, lamellÆ, the edges of which are undulated, and the intermediate spaces studded with minute dots. The eyes are smooth, and not granulose, as in Calymene. This genus is known in England by the name of the Barr Trilobite, from its occurrence in the limestone near Barr, in Staffordshire; it is sometimes five inches long, and three and a half wide (Geol. Surv. Decade 2, pl. iii. and iv.).

The genus Ogygia (Bd. pl. xlvi. fig. 9) is characterised by the elliptical and depressed form of the carapace, its nearly balanced extremities, and the prolongation of the buckler, or cephalic portion, on each side, into slender spikes, distinct from the body; the thoracic and abdominal regions are divided by two deep, longitudinal furrows, into three lobes; there is also a straight, longitudinal groove, in the front of the buckler (see figures and descriptions of O. Buchii, Geol. Surv. Decade 2). The Trilobites of this genus are found in the Lower Silurian rocks of North Wales and Ireland; they occur also in great abundance in the slate rocks of Angers, and some species are more than a foot in length.

Some species of the genus Phacops have long, pointed caudal appendages, as the P. (formerly Asaphus) caudatus (Lign. 177; Bd. pl. xlv. figs. 10, 10'; and Geol. Surv. Decade 2, pl. i.). The eyes are often well preserved, and each contains about 240 spherical lenses.

Trinucleus. Lign. 175, fig. 2; Ly. fig. 432.—This genus comprises several small forms which are found in the Lower Silurian rocks of England, and occur in the equivalent deposits of Sweden, Norway, and Russia.[485] In the Trinucleus, the cephalic shield is obtuse, trilobed, rounded, and terminating in lateral spikes; and its margin is marked by numerous pit-like depressions. There are six body-rings or thoracic segments. The caudal shield is large and somewhat triangular. There are no distinct eyes.

Paradoxides. Lign. 178.—The Trilobites of this genus are easily recognised by the ends of the lateral segments of the thorax and abdomen terminating in deflected points, which extend in spikes beyond the membrane they supported, and particularly those near the tail, which are much elongated; whereas in the other genera the lateral points of the segments are united by a membrane, which often forms a border beyond them. The cephalic buckler is semicircular, and its lateral angles are lengthened out behind into two strong spines; it is divided on the median line into four protuberances, by transverse grooves. The thorax consists of from sixteen to twenty segments; the abdominal buckler is generally very small and rounded. The animals of this genus have the body much depressed, and the lateral lobes wider than the middle lobe: some species are of considerable size, attaining several inches in length.

A very peculiar form of Trilobite (Brontes flabellifer, Ly. p. 348) is found in the Devonian strata of the Eifel and South Devonshire; the head, or cephalic region, is narrow, and has two lunated eyes; the thoracic region is trilobed and short, and composed of about ten small articulations; the abdominal very small, and bordered by segments, which radiate and form a wide, fan-shaped expansion. Other species of this genus occur in the Silurian rocks.

With regard to the under surface of the Trilobites much remains to be known. No decided indications either of antennÆ or extremities have been discovered. In an American specimen, Mr. Stokes detected a plate,[486] which appears to be a labrum, or upper mandible or lip, resembling that of Apus cancriformis. This animal has a similar labrum, "and lateral influted terminations of the shelly segments of the body, with a distinctly trilobed pygidium (tail or caudal portion), and a prolonged tail: the feet being foliaceous, and the abdomen merely covered by a membrane."[487] In the upper or dorsal surface of the carapace the Trilobites approach certain Isopoda, particularly in the characters of the buckler and eyes. Mr. Macleay states that among the existing crustaceans there are certain genera which individually possess some one or more of the characters, which have been thought peculiar to the extinct Trilobites. Thus the Serolis (Bd. pl. xlv. fig. 6), and the Bopyrus, have a trilobed form; the female CymothoÆ have the coriaceous margin of the body, and in some species are without eyes as are many of the Trilobites; while the eyes of the males of some CymothoÆ are composed of large facets, and are situated on the back of the head, wide apart, as in the Calymene; rudimentary feet, and the absence of antennÆ occur in Bopyrus; and lastly, the SphÆroma has an onisciform body, and the power of rolling itself up into a ball, like the Calymene (Lign. 175, fig. 4). The analogy between the Bopyrus and the Barr Trilobite is so close, that if the latter had a body with thirteen equal segments, and short crustaceous feet, it would be in every essential particular a male Bopyrus.[488] Burmeister regards the Trilobites as being related to the Branchipus. From the absence of eyes in the female, and their presence in the male of certain recent genera of crustaceans, it is not improbable that a similar character may have prevailed in the Trilobites, and that certain fossils referred to different genera, from the presence or absence of eyes, may have been the males and females of the same species.

The habits of the Trilobites, as deducible from Mr. Macleay’s exposition of their structure and affinities, must have resembled those of the CymothoadÆ, some of which, like the Calymenes, coil themselves up, and are not parasitical; while their close affinity to Bopyrus, and the apparent absence of distinct crustaceous feet, imply that they were to a certain degree sedentary. The flat under surface of their bodies, and the lateral coriaceous margin of several species, which is so analogous to that of the multivalve shell Chiton, render it probable that they adhered by a soft, articulated, under surface, to the rocks or sea-weeds. Their instruments of progression are unknown; whether they moved by means of membranaceous feet, or by the undulations of setigerous segments, like the earth-worm, or by wrinkling the under surface of the abdomen, like the Chiton, are questions yet to be determined. It is evident, from their longitudinally trilobed form, and lateral coriaceous margin, that they had the power of firmly adhering to flat surfaces; and while thus sedentary the thin but hard dorsal crustaceous shell would protect them from the attacks of their enemies. "The Trilobites, probably, like the Chitones, adhered in masses one upon another, and thus formed those conglomerations of individuals which are so remarkable in certain rocks; but it is not likely that they were parasitical, since almost all the existing parasites that adhere to other animals, have strong feet, armed at their extremities with hooks for that purpose."[489] From the form of the labrum of the mouth (Barrande, pl. i. and ii A) it is inferred that they were carnivorous, preying on naked mollusks, or on the annelides, with which their remains are associated.

As the compound eyes of the Trilobites[490] are similar to those of existing crustaceans and insects (see Wond. p. 792), the highly interesting and important fact is established, that the mutual relations of light to the eye, and of the eye to light, were the same in the remote epoch when the Trilobites flourished, as at the present time; and that the condition of the waters of the sea, and the atmosphere, and the relation of both these media to light, have undergone no change through the countless ages that have elapsed since the deposition of the Silurian strata.[491]

Geological Distribution of Fossil Crustaceans. We have seen that the Tertiary strata contain the remains of many of the highest organized crustaceans; a few brachyurous, macrurous, and entomostracous genera appear in the Cretaceous, Oolitic, and Liassic formations; whilst the Isopodous ArchÆoniscus and several species of Cypris occur in the Wealden and Purbeck deposits. Some few Entomostraca have been enumerated from the Trias and Permian.

One species of macrurous decapod has been found in the Muschelkalk of Germany; and Mr. Prestwich’s "Apus dubius" (Geol. Trans. 2d ser. vol. v. pl. xli. fig. 9), and Dr. Ick’s crustacean, noticed in Journ. Geol. Soc. vol. i. p. 199, both from the Coal Measures of England, are probably true Decapodous Crustaceans. With these exceptions not a species of the numerous tribes of Crabs, Lobsters, &c. has been observed in the older formations, though composed of such enormous thicknesses of marine detritus, and containing countless myriads of the relics of the inhabitants of the ocean.

A few species of Limulus, several Cytheres and allied genera, and a few Trilobites (Phillipsia and Griffithides) belong to the strata of the Carboniferous System. In the Devonian System we find some minute entomostracans, the gigantic Pterygotus, and various Trilobites (Brontes, Cheirurus, Homalonotus, Phacops, &c.); but it is the Silurian rocks that constitute the grand mausoleum of those ancient beings, the Trilobites.

There are about thirty genera of Trilobites found in the Silurian rocks of Great Britain and Ireland. Many of these are common to the Upper and Lower Divisions of that system; and some of them are met with both in the Silurian and in the Devonian rocks, as Phacops, Brontes, Cheirurus, Harpes, and Homalonotus. The Calymene Blumenbachii (Lign. 175, figs. 3 and 4) ranges through the Ludlow and Wenlock, to the Bala and Llandeilo formations. The Phacops caudatus also (Lign. 177), the Cheirurus bimucronatus,[492] and the Encrinurus punctatus[493] extend from the Ludlow, to the Llandeilo formation. The Upper Silurian rocks exclusively contain some peculiar forms, as Encrinurus variolaris, Bumastus Barriensis, and several species of Acidaspis. And the Lower Silurian has several distinct genera, namely, the Trinucleus (Lign. 175, fig. 2), Ogygia, Agnostus, Asaphus, Olenus, Remopleurides, &c. One species of Pterygotus, and one of Eurypterus, the Ceratiocaris and Hymenocaris, and several species of the minute bivalved Entomostraca (Leperditia and Beyrichia) are all that remain to be enumerated as constituting, in company with the Trilobites, the Crustacean fauna of the ancient Cambrian and Silurian seas.[494]

On Collecting Fossil Crustaceans.—The Crabs and Lobsters of the argillaceous tertiary strata are generally imbedded in nodules of indurated clay and septaria. On the shore beneath the cliffs on the north of the Isle of Sheppey, and near Southend, specimens may be observed in the nodules that have been exposed to the action of the waves, the attrition to which they have been subjected having partially worn away the surrounding stone, and displayed the enclosed fossils. In these examples the carapace is occasionally seen on one side, and the pair of pincer-claws on the other face of the boulder; the other feet and the plates of the thorax may sometimes be developed in such examples by chiselling away the enveloping mass. In the laminated marls of the tertiary and other deposits, in which the minute crustaceans, as the Cyprides abound, thin slabs covered with these relics may be easily extracted; and many of the tertiary clays and sands yield Cytheres, together with Foraminifera and other minute fossils, on careful washing and examination with a lens.

The Chalk crustaceans, particularly those which are muricated, or beset with spines and tubercles, as the Enoploclytia Sussexiensis and E. Leachii (Lign. 169), require considerable patience and dexterity to develope successfully. The crustaceous covering of the carapace and claws adheres firmly to the chalk by the rough external coat, while the inner, smooth, glossy surface as readily separates. Hence, upon breaking a block of chalk containing portions of these crustaceans, we find one piece exhibiting a chalk cast of the claw or carapace, covered with tubercles or papillÆ, that have been moulded in the bases of the spines of the crust; and on the other portion the crustaceous shell imbedded by its outer surface, and presenting the internal glossy lining, beset with circular depressions, which are the bases of the spines. This crust is exceedingly friable, and will flake off by a very slight touch. To obtain specimens with the external characters, it is necessary to proceed with great caution; and when indications of a crustacean are observed in a block, the chalk should be chiselled or sawn off to within half an inch of the surface of the fossil, and the remainder of the stone be cleared away, piece by piece, by means of a penknife or graver. By this process the fossils figured Foss. South D. pl. xxix. xxx. xxxi. were developed. When a fine specimen has been broken, and the shell is attached to one piece of the stone and the cast to the other, it is possible to obtain an illustrative example of the external surface, by cementing the pieces accurately together with very thin hot glue; and, when firmly consolidated, the chalk may be removed, and the spines, tubercles, and papillÆ of the crustaceous covering be developed by the method previously described. A thin coating of mastic varnish will give durability to the crust, and improve its appearance; but the rich brown colour it possesses when first exposed soon disappears. The Crustaceans of the Galt are often found amongst the argillaceous and pyritous nodules flung aside in heaps where the Galt is used for brick-making.

The CytheridÆ of the Chalk, Galt, Oolite, &c. are to be obtained by disintegrating the matrix in water, and examining the debris, after sifting, under a lens.

The Limuli of the Coal-measures often form the nuclei of clay nodules, as in the example figured Lign. 172, in which fig. 2 represents the nodule without any external indication of its contents, and figs. 1, and 3, the same broken, and displaying the crustacean. Traces of the legs, branchiÆ, and other appendages, should be diligently sought for in fossils of this kind, for they are more likely to be detected in such specimens than in those found in limestone. It is possible that polished sections of the coiled up examples of Trilobites (Lign. 175, fig. 4) would throw some light upon the nature of the hitherto undiscovered organs of locomotion and respiration of this extinct order of Crustaceans.

A FEW BRITISH LOCALITIES OF FOSSIL CRUSTACEANS.

Abberley. Silurian: Trilobites and Beyrichia.

Aberystwith, neighbourhood of. Silurian: Trilobites.

Arundel, Sussex. Chalk-pits in the vicinity. AstacidÆ and CytheridÆ.

Atherfield, Isle of Wight. Wealden: Cyprides in clay (Lign. 174).

Barr, Staffordshire; limeworks at Hay Head. Silurian: Trilobites, particularly of the genus Bumastus.

Bewdley, Shropshire. Silurian: Trilobites.

Bolland, Yorkshire. Carboniferous Limestone: Trilobites (Cyclus, Phillipsia).

Burdie-house, near Edinburgh. Fresh-water coal-measures. Cyprides and Eurypteri.

Burham, near the banks of the Medway, Kent. Quarry of Mr. W. Lee, a good section of the lower Chalk: fine Crustaceans.

Coalbrook Dale. Coal-measures and Silurian. Limuli and Trilobites.

Coniston, Lancashire. Silurian: Trilobites.

Dinley, Wilts. Purbeck. Isopoda (Lign. 171) and Cyprides.

Dover. In the lower Chalk, Astacus (Enoploclytia) Sussexiensis, &c.

Dudley. Upper Silurian: Trilobites in abundance.

Durlstone Bay, near Swanage. Purbeck: Cyprides and Isopoda.

Folkstone, Kent. In Galt: small Crabs (Lign. 168), and numerous Cytheres.

Grays, Essex. Pleistocene: Cyprides.

Gristhorpe Bay, Yorkshire Oolite: AstacidÆ.

Hastings, Sussex, neighbourhood of. Wealden: Cyprides.

Hollington, near Hastings. Wealden: Cyprides.

Hordwell Cliff, Hampshire. Upper Eocene: Cyprides.

Kildare, Ireland. Carboniferous and Silurian: Trilobites.

Langton Green, near Tunbridge Wells. Wealden: Cyprides.

Lewes, Sussex. In the Chalk-pits of the vicinity: AstacidÆ (Lign. 169), and other Crustaceans.

Llandeilo, Caermarthenshire. Lower Silurian: Trilobites, Trinuclei.

Lyme Regis, Dorset. Green Sand: Hoploparia. Lias: Coleia.

Malvern Hills. Lower Silurian. Trilobites (Olenus).

Meifod Hills, Montgomeryshire. Silurian: Trilobites.

Mount Pleasant, Caermarthen. Silurian: Trilobites.

Newton Bushel. Devonian: Trilobites (Brontes).

Rhiwlas, near Bala, North Wales. Lower Silurian: Trilobites.

Ringmer, near Lewes. In Galt: small Crabs, &c.

Sandown Bay, Isle of Wight. Cyprides, in Weald Clay.

Scarborough. Oolite: AstacidÆ, in clay nodules.

Sheppey. London Clay: Lobsters and Crabs.

Steyning, Sussex. In Chalk-marl: Lobsters, &c.

Tyrone, Ireland. Carboniferous and Silurian: Trilobites.

Wenlock, neighbourhood of. Upper Silurian: Trilobites.

Westbury, Gloucestershire. Lias: Estheria and Cyprides.

Wilmington, near Marton, Salop. Silurian: Trilobites.

Wistanstow, Salop. Lower Silurian: Trilobites.

Worthing, Sussex. Neighbouring Chalk-pits. Lobsters, &c.

FOSSIL INSECTS, SCORPIONS, AND SPIDERS.

From the Crustaceans we pass by a natural transition to the other Articulata, viz. the Arachnida (Scorpions and Spiders) and the Insecta, in the last of which "the highest problem of animal mechanics is solved, and the body and its appendages can be lifted from the ground and propelled through the air" (Owen). The skeleton in these animals, as in the Crustaceans, is chiefly external, and consists of a hard shell or case (composed of a peculiar substance, termed chitine), divided into segments, and furnished with articulated or jointed hollow extremities. The head is distinct, and has a pair of compound eyes, and of jointed antennÆ. To the segments that form the thorax the legs are attached, and these consist of three pieces in the hexapods (insects with six feet), each supporting a pair of feet. The wings in the flying insects are attached to the middle and third thoracic segments. The legs, or articulated appendages, are hollow, as in the Crustaceans, and contain the muscles and other soft parts. The generic and other distinctions adopted by naturalists, to facilitate the study of this most numerous division of the animal kingdom, are founded on the structure and configuration of the antennÆ and wings. The latter consist of flat membranous expansions, supported by hollow tubes or nervures; and in some orders consist of one pair, and in others of two. In burrowing insects, as the Beetle, the front pair of wings constitutes a hard case (elytron), which covers and protects the membranous posterior pair, when the animal is in repose or walking. The modifications of the wings furnish the characters by which the class is divided into orders. Thus the Coleoptera (sheathed-wings) comprise the beetles and other burrowing insects, in which the membranous wings are folded transversely beneath the elytra, or wing-cases. The Orthoptera (straight-wings), those with two pairs of wings, of which the anterior encase the others, the posterior being membranous, and folded longitudinal during repose; as the Earwig, Cockroach, Mantis, and Locusts. Neuroptera (nerved-wings), those with two pairs of transparent reticulated wings, as the Libellula, or Dragon-fly, the Ephemera, and the Termites. Hymenoptera (membranous-wings), with simply veined membranous wings, as the Gall-flies, the Bee, &c. The Cicas, Aphis, and Coccus constitute the somewhat anomalous group termed Homoptera (equal-wings), in which the anterior pair of wings are usually similar to the posterior in consistence, and shut up in a roof-like manner. The Heteroptera (different-wings) include the Nepa, Notonecta, &c. and have the anterior wings coriaceous at the base, membranous towards the point, and shutting up nearly horizontally, partly lapping over one another. Lepidoptera (scaly-wings) have wings covered with scales, as the Butterfly and Moth. In the Diptera (two-wings) the anterior pair of wings only are the instruments for flying, and the hinder pair are reduced to mere clavate appendages, as the Gnat and Fly. The PhryganeÆ (Caddis flies) constitute the order of Trichoptera (hairy-wings), related to the Neuroptera, but resembling the Lepidoptera in the distribution of the nervures of the wings, and in many other characters. Lastly, there remain the Wingless Insects, divisible into three orders, of which the Flea, the Parasites, and the Podura are respectively the types. With these few remarks on those durable parts of the structure of Insects which their fossil remains generally present, we must quit this part of the subject, and enter upon the examination of the relics which are the immediate objects of our present inquiry.

From the enduring nature of the elytra, segments, and articulated extremities of insects, the fossil remains of animals of this class might naturally be expected to abound in lacustrine and fluviatile deposits; this, however, is not the case, and except in a few favoured localities, fossil insects are seldom met with, and good specimens rank among the most rare and interesting of the organic remains of the Secondary formations. In certain Tertiary beds, as at Œningen, and Aix in Provence, insects of numerous species and genera have been discovered; and the cream-coloured limestone of Solenhofen, among its numerous other treasures, has yielded some fine examples of this class. The strata in which remains of insects have been found in England[495] are the Tertiary clays of the Bagshot series, the Hastings beds, Purbeck marls and limestones, Kimmeridge Clay, Oxford Clay, Forest Marble, Stonesfield Slate, Upper and Lower Lias, and the Coal Measures.

[495] PalÆontologists are particularly indebted to the Rev. P. B. Brodie, F.G.S. for his compendious and valuable "History of the Fossil Insects in the Secondary Rocks of England" (8vo. 1845); and to J. O. Westwood, Esq. the eminent Entomologist, for the very important and interesting Observations on the Insect Remains, prefixed to the above work. In an interesting paper on the Geology of the vicinity of Ilminster, C. Moore, Esq. has noticed the numerous Insect remains of the Upper Lias of that place. Prof. E. Forbes and W. R. Binfield, Esq. have discovered Insects in the Hastings series; and Mr. Binfield, besides having most successfully searched the Upper Lias of Gloucestershire, has also detected some specimens in the Lias at Lyme. Lastly, Mr. Morris has found Insects in the Upper Lias in Lincolnshire.