  FOSSIL TESTACEOUS MOLLUSCA, OR SHELLS. Lign. 120. Fossil Oyster, from the Chalk. Kemptown, Brighton. On Fossil Mollusca.—Numerous as are the fossil remains of the various types of animal organization which have already passed under review, they are far exceeded in number and variety by those of the beings whose mineralized relics we now propose to investigate. Although every one is familiar with the external appearance of the shells cast up by the waves on the shores of our island, and of those which, from their varied colours and elegant forms, are preserved in Except as shedding some light on the structure and economy of their inhabitants, the shells, in the estimation of the naturalist, are the least interesting part of the organization of the Mollusca; but to the geologist, from their permanent nature, and the proofs they yield of the conditions under which the strata that contain them were deposited, they are important in the highest degree. It has even been found convenient to classify formations, in which fossil shells largely prevail, by the relative numerical proportion of the recent and extinct species found in the different groups of strata; and the terms, Eocene, Miocene, and Pliocene, (proposed by Sir C. Lyell,) have reference to this character, as we have previously explained (ante, p. 24.). FOSSIL MOLLUSCA. The Mollusca, a name indicative of the soft nature of the integuments of these animals, constitute a very comprehensive subdivision of the animal kingdom, and are separable into two principal groups, viz. the Acephala and the Encephala. I. The Acephala (so termed because they are destitute of a head) have neither jaws, tongue, nor a distinct mouth. They are aquatic, and are subdivided into classes, according to the modification of their integument, or of their gills. a. The Tunicata (from the elastic tunic, or mantle, in which they are enclosed) have no shell, and therefore do not b. The Brachiopoda (arm-feet) have two long spiral fleshy arms, or brachia, developed from the sides of the alimentary orifice, are enclosed in bivalve shells, and respire by means of their vascular skin, or mantle. They have not the power of locomotion, but are fixed by a peduncle to other bodies. c. The Lamellibranchia (plated gills) have also bivalve shells, but their respiration is effected by gills composed of vascular membrane disposed in plates, and attached to the mantle; the beard of the Oyster is the branchial or respiratory apparatus of that animal. These bivalve Mollusca are subdivided into those which close their shells by one adductor muscle, hence called monomyaria, as the Oyster; and those which have two muscles, dimyaria, as the Cockle. As the impressions left on the shells, by the attachment of these adductor muscles, and by the margin of the mantle, are found as perfect in the fossil as in the recent, they constitute important distinctive characters. Dr. Gray's definition of the respective parts of univalve and bivalve shells is at once clear, concise, and natural, being conformable to the structure of the body of the enclosed mollusk. The front of the shell is the part which covers the head of the animal; the back of the shell is the part which covers the tail; the left and right sides correspond with the same parts of the mollusk. In univalves, the apex of the shelly cone whether it be FOSSIL BIVALVE SHELLS. Lign. 121. Illustration of Fossil Bivalve Shells; nat. Petricola Patagonica. D'Orb. Interior of right valve, and the same valve with the animal as seen on the removal of the left valve.
(The length of the shell is estimated from o to p, its breadth from l to n.) In bivalves (Lign. 121) the ligament is always on the dorsal surface of the animal, and the mouth in front of the apex or umbo of the valves, before the ligament. A bivalve placed with the hinge side uppermost and the ligament II. The Encephalous Mollusca.—These possess a head, with feelers or soft tentacula, eyes, and a mouth with jaws; they are arranged in classes, according to the modification of their locomotive organs; for, with but few exceptions, they are free animals, and can crawl, climb, or swim. Their shells are, for the most part, composed of one piece, or valve, hence they are termed Univalves. In some genera the shell is a simple cavity, spirally disposed, as in the Snail; in others, it is conical, consisting of one or many pieces, as in the Limpet and Chiton. In the Cephalopoda it is internally divided into cells, or chambers, as, for example, in the Nautilus. The Encephalous Mollusca are subdivided into the following classes; viz.— a. Pteropoda (wing-feet).—In these the organs of progression are two wing-like muscular expansions, proceeding from the sides of the neck, by which they can swim and float in the open sea: all the species are of small size. b. Gasteropoda (feet under the body).—These crawl by means of a muscular disk, or foot, which is attached to the under-part of the body; most of the species are marine, but some are terrestrial, and others inhabit fresh-water. They are very widely distributed; the garden snail is a familiar instance of a terrestrial Gasteropod. c. Cephalopoda (feet around the head).—The mollusca of FOSSIL MOLLUSCA. In many univalves the aperture or opening is entire, that is, without any notch or groove; in others it is notched or extended into a canal, or siphon, and this character has relation to the respiratory organs: thus the Gasteropods, in which the water is conducted to the interior by a muscular tube, or siphon, have the margin of the aperture of the shell channelled; as in the Whelk, or Buccinum. Many of the land and fresh-water species have entire openings, and are, for the most part, herbivorous; while the greater number of the marine univalves have the aperture indented or notched, and are carnivorous. In the generic distinctions of the simple univalves, the form of the mouth is an important character; while in the bivalves, the configuration of the hinge affords an equally convenient aid for their classification. Some tribes of testaceous mollusca are exclusively marine; many are restricted to the brackish water of estuaries; others live only in fresh-water; and some on the land. Their geographical distribution is alike various: certain groups inhabit deep water only, and are provided with means by which they can maintain themselves near the surface of the ocean, far away from any shore; while others are littoral, that is, live in the shallows along the sea-shores. Many exist in quiet, others in turbulent waters; some are gregarious, like the oyster; while others occur singly, or in groups. The vertical range, that is, the relative depths in which the mollusca live in the sea, is also strictly defined; certain genera being, in a great measure, restricted to moderate depths, others to a few fathoms, and many to the profound abysses of the ocean, which neither the dredge nor the plummet can reach. All these varieties of condition are more or less strongly impressed on the shells, which may be considered as external skeletons; The number of living species of mollusca known to naturalists, not including the shell-less genera, exceeds twelve I must restrict myself to a brief account of some of the most common genera that occur in the British strata; and shall dwell more particularly on those species which prevail in the secondary formations, because they present the most important deviations from the recent types that are familiar to the general observer; by this means, and by reference to figures in standard works, the collector will, I trust, be enabled to identify the fossil shells which may most frequently come under his notice in the course of his geological rambles. FOSSIL BIVALVE SHELLS; INCLUDING THE BRACHIOPODA AND LAMELLIBRANCHIA. FOSSIL BIVALVE SHELLS. Although in the modern Tertiary strata, as the Crag, and in the arenaceous beds of the Eocene formations, shells are generally found in so perfect a state, that no caution or knowledge is requisite for their collection, yet a few preliminary remarks are necessary to point out certain conditions in which the remains of mollusca, or evidence of their existence, occur in the mineral kingdom, and particularly in the older fossiliferous rocks. Shells are found in the strata in the three following states:— 1stly. Shells in which the constituent substance has undergone but little change. Many of the specimens in the 2dly. The form preserved, but the constituent substance mineralized. This state is very common in shells that are imbedded in hard rock, whatever may be the age of the deposit. In calcareous strata the testaceous substance is generally transmuted into calcareous spar, as in most of the specimens from the chalk, oolite, mountain limestone, &c. In sands abounding in silex, the shell is changed into flint, as in the exquisite fossils from the Greensand of Blackdown, Devonshire; in deposits permeated with sulphuret of iron, the shells are often metamorphosed into pyrites, as in the Ammonites in the Lias, Galt, &c. 3dly, In the state of casts and impressions. Although in loose sand the shells are either empty, or filled with detritus easily removable by washing; in clay, limestone, and sandstone, the cavities are generally occupied by consolidated materials, which had entered when in a soft or fluid state; and frequently the substance of the shell has disappeared, and the stony cast of the interior alone remains. In many instances, the spaces left by the dissolution of the shells are filled with spar, or the casts are closely invested by the surrounding stone, from long-continued superincumbent pressure while the matrix was in a plastic state; and in such cases the casts are often distorted and flattened. But the vacancy is occasionally empty, and on its walls is found an impress of the external surface of the shell, with all the lines and ornaments of the original as sharp as if cast in plaster of Paris. Lign. 122. TurritellÆ, from Bracklesham, Sussex. Tert.
SEPTARIUM WITH SHELLS. The specimen, Lign. 122, fig. 2, from the tertiary strata at Bracklesham Bay, Sussex, is a polished slice of indurated argillaceous limestone, from a septarium (nodule divided by fissures), abounding in spiral univalve shells, called TurritellÆ. Fig. 1 is a perfect shell of the same species, extracted from soft clay; and fig. 3, a cast in calcareous spar, obtained from the septarium. In the polished slab, fig. 2, sections of numerous shells are seen. The dark partitions, The polished slab of the Septarium, Lign. 122, fig. 2, demonstrates another condition of fossil shells—that of a compact argillaceous limestone—and entire beds of marble are composed of an aggregation of this kind, formed of shells and other animal exuviÆ, consolidated by mineral infiltrations. In the older secondary strata this state prevails; and the beautiful markings of many valuable marbles, are merely sections of the enclosed shells. But this process is not restricted to the deposits of ancient date; at the present moment the same operation is silently but constantly going on in our seas, and an examination of the specimen, Lign. 123, will afford an exemplification of the manner in which these shelly limestones are produced. BRIGHTON SHELL-CONGLOMERATE. Lign. 123. Shell-Conglomerate; now forming in the British Channel. Dredged off Brighton.
We have here a solid mass of stone, composed of several recent species of shells, corals, &c. It is a fragment of a large block, dredged up from the British Channel, off Brighton. Similar masses have been obtained at different soundings along this part of the Sussex coast; and in some specimens numerous other species of recent shells, as oysters, mussels, whelks, &c. enter into the composition of the consolidated rock. The shelly and coralline limestones and sandstones, so abundant in the ancient strata of England have been formed in a similar manner; and when the modern conglomerate of Brighton shall have been permeated with crystalline matter, and subjected to great pressure by Lign. 124. Shell-Limestone; from the mouth of the Thames.
MODERN SHELL-LIMESTONE. Off the Kentish coast, near the mouth of the Thames, a "The vast deposits of fluviatile shells which exist in Florida, at Picolata, Volusia, and Enterprize are of great geological interest. The two latter places present bluffs and hills of from forty to fifty feet in height, extending half a mile or more from the river, that are composed of scarcely anything but well-preserved shells of Paludina vivipara, Ampullaria depressa, some undetermined species of Unio, Helix septemvolvis, Melania, and a few others. There is but a scanty mixture of earth, and the shells are clean, and look as if they had been washed ashore after the death of their inhabitants. In some places the beds are sandy, and are hardening into a calcareous shelly sandstone. In one such bed the superficial stratum furnished a few bones of turtles and undetermined fragments, the bones of some large vertebrate animal. This is, I believe, the locality where Count PourtalÉs collected human bones in a recent sandstone.... No microscopical forms were detected in these beds after the most careful search." Lign. 125. Terebratula and Rhynchonella; nat. Chalk. Lewes.
Fossil Shells of the Brachiopodous Mollusca.—These are bivalve shells, of which nearly five hundred species are found in the British strata. They occur in incredible numbers in the ancient rocks, to which several genera are restricted; while some continue through all the formations, TEREBRATULA. Terebratula (bored, alluding to the perforated beak), Lign. 125.—The common species of this genus must be familiar to all who have ever looked into a quarry of Chalk, or of Shanklin sand, in the south-east of England. They have been humorously called the Fossil Aristocracy, from the incalculable antiquity of their lineage. The species are very numerous; more than 300 extinct forms have been determined. In the smooth TerebratulÆ, the laminations of the shell are full of minute perforations, which may be seen by a lens of moderate power; the appearance of this structure, Several species of Terebratula are found both living and fossil, e.g. Terebratula vitrea, living in the Mediterranean, fossil in Sicily,—T. caput-serpentis, recent in the British seas, fossil in the Crag,—and T. lenticularis, both recent and fossil in New Zealand. Lign. 126. Terebratula and Spirifer.
SPIRIFER. PENTAMERUS. Spirifer (containing spiral processes). Lign. 126.—In the Silurian, Devonian, and Carboniferous limestones there is a profusion of several genera of Brachiopoda, whose All these genera are extinct; they prevail in the oldest fossiliferous rocks, and gradually disappear as we ascend to the newer formations; the last trace of their existence is in the Lias, in which one species has been found. But the TerebratulÆ abound in the Lias, Oolite, Chalk, &c., occur in the tertiary formations, and several living species inhabit the seas around Australia and New Zealand. (See ante p. 390.) Rhynchonella, Fischer. The "plaited" TerebratulÆ differ from the typical species (e.g. T. australis, caput-serpentis, vitrea, &c.) more than even the Spirifers differ, and must be regarded as forming a distinct family, RhynchonellidÆ, which will include Pentamerus. The shell is not punctate; the arms are spiral, supported only at their origins by shelly processes; the larger valve is beaked acutely, and has a notch within the beak through which the pedicle passes; sometimes the notch is converted into a foramen, by two little plates, (deltidium,) as in Terebratula. The form of the RhynchonellÆ is tetrahedral. Lign. 125. Pentamerus, Ly. p. 352.—With the Spirifers, and other Brachiopoda of the Silurian System, some bivalves which, in their general figure, resemble certain species of TerebratulÆ, frequently occur. These shells differ in their internal structure from all other genera, in having a septum, or plate, by which their cavity is divided into four chambers; and in one valve the septum itself contains a cell, thus making five chambers, whence the name Pentamerus (five-celled). Orthis, LeptÆna, and Producta form a third family, with horizontal spiral arms, unsupported by shelly processes. Davidsonia is a LeptÆna attached by the ventral valve, and the only genus in this family which is fixed by the shell itself. Calceola. a genus of Brachiopoda; the shell of an inverted pyramidal form, the upper valve nearly flat; found in the Devonian strata of the Eifel, and in Devonshire. Crania, Ly. fig. 205. These are small brachiopodous shells, attached to other bodies; very frequently to the Echinites of the chalk. The free valve is commonly wanting, but I have found specimens dispersed in the rock. In many of the quarries in Kent and Sussex, the helmet Echinites bear groups of these shells. Ly. fig. 13. Orbicula. This genus resembles Crania in form, the upper valve being like a limpet, whilst the attached valve is flat; it differs, however, from Crania in being horny and flexible, and is fixed to rocks on the bed of the sea, by a muscular pedicle passing out through a small fissure. Species of Orbicula are found in strata of all ages, from the Lower Silurian to the Tertiary, and several are now living in tropical seas. Obolus. Eichwald. In the Lower Silurian (Obolite grit) of Sweden and Russia, is a Lingula, with a hinge and a notch for the pedicle; it has not hitherto been found in Britain. LINGULA. HIPPURITES. Lingula. Ly. p. 353, fig. 412.—The Brachiopoda referred to this genus have a long peduncle, and their respiratory apparatus has no calcareous support; the recent species burrow in the sand, being usually inhabitants of shallow waters. The LingulÆ aÆre readily distinguished from the TerebratulÆ by their imperforate, equivalved shells. One species is found in the Aymestry limestone, and several have been collected from the Mountain limestone, Oolite, and Shanklin sand. With reference to the species of Brachiopoda, particularly of the TerebratulÆ, which inhabit the depths of the ocean, Professor Owen observes, that "both the respiration and nutrition of animals, which exist beneath a pressure of from sixty to ninety fathoms of sea-water, are subjects suggestive of interesting reflections, and lead us to contemplate with less surprise the great strength and complexity of some of the minutest parts of the frame of these diminutive creatures. In the unbroken stillness which pervades those abysses, the existence of these animals must depend on their power of exciting a perpetual current around them, in order to dissipate the water laden with their effete particles, and to bring within the reach of their prehensile organs the animalcules adapted for their sustenance." Hippurites. This genus belongs to a group of fossil shells whose characters are somewhat problematical, some conchologists referring them to the ordinary bivalves, and others to the Brachiopoda. Although Hippurites have not been discovered in the British strata, I am induced to notice them in this place, in consequence of their great abundance in the Cretaceous deposits of the South of France, and in the Oolite of the Pyrenees; and also to illustrate the nature of a nearly related genus, SphÆrulites, of which one or more species occur in the Sussex Chalk. The Hippurite is of an elongated conical form, and fixed Fossil Shells of the Lamellibranchia.—These are bivalve shells, the animals of which differ from the preceding class, as we have already stated, in performing respiration by means of lamellated gills. The valves are united by a strong substance, termed the ligament, which, by its elasticity, admits of the shells being opened to a considerable extent; and they are closed by powerful, short, thick muscles, called adductors. The shells of some of the genera, as the Oyster and Scallop, have but one muscle, (monomyaria); others, as the Cockle, or Cardium, and Venus, have two, (dimyaria); and by these characters the class is arranged in two groups. Monomyaria: Bivalve Shells, with one muscular impression. FOSSIL OYSTERS. Ostrea, Lign. 120.—The Oyster is well known to possess no power of locomotion; it is attached to rocks, pebbles, and other bodies, and forms extensive beds, consisting of numerous individuals, of all sizes. There are many fossil species; the British strata yield between forty and fifty. In some localities. Oysters are found in thick beds, of great extent, apparently on the spots they occupied when living. One of the most interesting localities I am acquainted with, is Sundridge Park, near Bromley, in Kent, where a hard conglomerate, entirely made up of oyster-shells, and the shingle that formed their native bed, is quarried. This stone is much employed for ornamental rock-work, and several walls in and near Bromley are constructed of it: these display the fossils, some with the valves closed, others open, others detached, and the whole grouped as if artificially imbedded to expose the characters of the shells. These oyster-beds belong to the tertiary strata of the London basin; they extend to Plumstead, and other places in the vicinity; and in some localities, the oysters are associated with other bivalves, called Pectunculi. In the tertiary clays near Woolwich and Bexley, fossil oyster-shells abound. In the neighbourhood of Reading, in Berkshire, an extensive layer of fossil oysters occupies the same geological position, namely, the lowermost sands and clays of the London basin. Wherever the strata around London are perforated to a sufficient depth, this oyster-bed is reached. Very recently an Artesian well was bored at Hanwell, in Middlesex, and at the depth of two hundred and eighty feet this stratum of sand with oyster-shells was found. At Headley, near Reigate, in Surrey, there is a similar deposit. These oysters very closely resemble the edible species. The White Chalk contains several species of Ostrea, but I believe no beds of these shells have been found in it; on the A small oyster, called Ostrea vesicularis, is a characteristic shell of the chalk; one valve is convex, the other flat; it is abundant in the Chalk of Norfolk, and also in the Firestone of some localities: it is figured Ly. p. 212. Another small species, having the margin plicated (O. plicata), is also frequent in the Chalk. A large shell, with the margins deeply indented by angular folds, resembling the recent cockscomb oyster, is abundant in the Chalk Marl and Firestone; particularly near Dover, and around Selbourne in Hampshire, where it attracted the notice of White, by its resemblance to the living "Cockscomb Oyster" of the West Indies; it is named Ostrea carinata, and figured Ly. p. 212, fig. 204. One other species may be noticed, the Ostrea deltoidea, which has been found in every locality of the Kimmeridge Clay in England and France. It is a very flat species, and of a triangular form; the specific name is derived from a supposed resemblance to the Greek letter ?, delta. I believe that in England no shells of this genus have been observed in strata older than the Lias. Lign. 127. Shells and Echinite from the Oolite and Lias.
GRYPHYÆA. Gryphya. Lign. 127, fig. 6.—The shells to which the term GryphÆa, or Gryphites, is applied, are related to the Oyster, but distinguished by the deep concave under valve, and its curved summit, or beak, and the almost flat, or opercular upper shell. The Gryphites are of a finer laminated structure than the oysters, and the ligament of the hinge is inserted in an elongated curved groove. There are about thirty British fossil species, none of which have been SPONDYLUS. PLAGIOSTOMA. Spondylus. Lign. 128.—A species of this genus is so frequent in the Chalk, that it ranks with certain TerebratulÆ, as characteristic of that formation. One valve is covered with long slender spines, which, in the usual examples, are destroyed by the mode of extracting them. The specimen figured shows the appearance of a shell partly cleared; the remainder of the chalk might be removed by a penknife (taking care to leave the longest spines supported by brackets of chalk), and it would then resemble the beautiful fossils figured Min. Conch. tab. 78, and in Geol. S. E. p. 125. Between the beaks there is a triangular aperture in the spinous valve, which some naturalists, with much probability, suppose was once filled up with shell, as in the recent species. Lign. 128. Spondylus spinosus. In Chalk-flint. Lewes. In the cretaceous strata of North America, Dr. Morton has discovered a Spondylus (S. dumosus) very nearly related to S. spinosus; but it differs in its general form, and has both valves beset with strong spines. I have the fragment of a large bivalve from the Kentish Rag (Mr. Bensted's quarry), which has the peculiar structure of the Water-clam (Spondylus varius of Mr. Broderip); namely, hollow interspaces formed by shelly layers or partitions, which were secreted by the posterior part of the mantle, or investing integument of the animal, as it gradually receded from that part of the shell. In the recent Water-clam the cells are full of fluid. Plagiostoma, Llhwyd, 1699. This genus, adopted by Mr. Sowerby in the Mineral Conchology, is scarcely distinguishable from Lima of Bruguiere (1791). Most of the recent species are ornamented with small asperities, from which the name lima (file) is derived; they are symmetrical shells attached by a byssus. Several smooth species of this genus are found in the Chalk, Plicatula, is another genus of this family, of which there are three British fossil species. A delicate shell, with slender depressed spines (P. inflata. Foss. South D. pl. xxvi.), occurs in the Chalk Marl. The recent species are natives of the seas of warm climates. Pecten.—The common scallop-shell will serve as a type of this genus. The animals of these shells, unlike the oysters, have the power of locomotion, and when in the water, may be seen moving with rapidity, and flapping their shells to and fro with great activity. Numerous species are found fossil. In the Pliocene, and other marine tertiary deposits, Pectens abound; in the White Chalk there are several elegant forms (see Foss. South D. plate xxv.); many kinds in the Oolite and Lias; and several in the Devonian strata. A large Mediterranean species (Pecten JacobÆus, Ly. p. 152) occurs in the Pliocene strata of Palermo, in every stage of growth, and as perfect as if recent. The Chalk and Shanklin sand contain a small inequivalved Pecten, the lower valve of which is convex, and pentangular, the upper flat, and both strongly ribbed, or pectinated; it is named Pecten quinquecostatus (Foss. South D. pl. xxvi. Ly. p. 212); and in the cretaceous strata of North America a variety of this species is found. In the Chalk Marl a large and beautiful Pecten (P. Beaveri. Lign. 129 Inoceramus Cuvieri. Chalk. Lewes.
INOCERAMUS. Inoceramus. Lign. 129.—This name, which refers to the fibrous structure of the shell, has been given to a fossil genus, of which there are about thirty species in the cretaceous In the Galt, or Folkstone-marl, two small species of this genus are to be found in every locality I have visited. They were first figured and described by Mr. Parkinson, under the name of Inoceramus sulcatus, and I. concentricus (Wond. p. 330, fig. 1 and 3). In most examples the shell is in Lign. 130. Flint, with fragments of Inoceramus. Chalk. Lewes. a. Marks the section of a fragment of shell, with numerous cavities, occasioned by the depredations of Cliona Conybearei. b. Portion of shell partially decomposed, and exposing siliceous, globular bodies, connected by filaments, which are flint casts of the hollows left by the Cliona. The shells of the Inocerami, like those of the oyster, and other living mollusca, were exposed to the attacks of some parasite, and perhaps of some Annelid, as the Nereis. The shells are often cellular from this cause, and the cavities are found either hollow, or filled with chalk, or, as in the example Lign. 130, with flint. In the latter case, upon the decomposition of the shell, the siliceous casts remain in relief on the surface of the flint, as in Lign. 130, b. Such specimens are common in the broken flints of the South Downs, and in the shingle on the sea-shore of chalk districts; Avicula. Lyell, p. 274.—Above fifty species of this genus of shells have been found in the British strata; their general character will be readily understood by reference to the pearl-oyster, (Avicula margaritifera,) which is so largely imported for the manufacture of mother-of-pearl ornaments. A remarkable species is found in the Lias, called, from the great disproportion in the size of the shells, Avicula inÆquivalvis, (Lyell, p. 274.) The recent species are inhabitants of warm climates. Our limits will not admit of further notice of the Monomyaria, and we proceed to the second division of the plated-gilled mollusca. Dimyaria: Bivalve Shells, with two muscular imprints. The conchifera, or bivalve shells, of this group, found fossil, are more than double in number those of the preceding; nearly eight hundred species are known in the rocks of Great Britain, of which by far the greater number is marine. But we must restrict our notice of this division to a few genera, that more space may be devoted to that important class, the Cephalopodous Mollusca. The Cardium, Venus, and Mussel shells, are familiar examples of the Dimyaria. The conglomerates, now forming in the British Channel, from accumulations of the recent species of Cockle (C. edule), have been previously noticed; see Lign. 124, p. 386. In the strata of England VENERICARDIA. PECTUNCULUS. Venericardia. Ly. p. 199.—These shells are abundant in the tertiary strata; one large species, V. planicosta, (Ly. p. 199, fig. 171,) is found in immense quantities in the clay and sand at Bracklesham Bay, in Sussex, from the young to the adult state; some examples are very large, and perfect. In the sand at Grignon, near Paris, the same shell is abundant, possessing the usual white and delicate aspect of the fossils of that celebrated locality of the Calcaire grossier. Only one species has been noticed in the British secondary strata. Pectunculus. Wond. p. 244, fig. 8.—In the London clay at Bracklesham Bay, Highgate, Hordwell Cliff, and in the arenaceous limestone of Bognor rocks, an immense number of the bivalve shells, called Pectunculi (little pectens), occur. Some of the French marine tertiary strata also abound in the same, and other species of this genus. In the above-mentioned Sussex localities, these shells are so numerous, as to be the most frequent fossils that come under the notice of the collector. They are readily known from their associates by their rounded equivalve shells, and the single arched row of teeth along the hinge, resembling Nucula.—Several species of a small elegant bivalve, related to the preceding, but distinguished by having two rows of teeth on the hinge, diverging from an interspace between the beaks, are found in the Crag and other tertiary deposits (Min. Conch. tab. 180, 192). Two species occur in the Galt (Foss. South D. pl. xix. fig. 5, 6, 9), at Ringmer, Folkstone, Bletchingley, &c., sometimes with the shell perfect, but generally in the state of casts composed of indurated clay, and having impressions of the muscles and of the two rows of hinge-teeth. The shell of one species is marked with fine transverse grooves, or striÆ (N. pectinata); the other is of a flattened ovate form, and the surface smooth (N. ovata). The most beautiful species of Nucula are the N. bivirgata of the Galt of Folkstone, and F. CobboldiÆ of the Norwich Crag. The species of Nucula with the posterior side produced into a long beak have been separated under the name Leda; they have a pallial sinus, indicating a siphon to the mantle;—
PINNA. MYTILUS. MODIOLA. Pinna.—The common large Pinna, of the Mediterranean, is well known, and differs so entirely from other shells, as to Mytilus, or Mussel.—There have been found about twenty species of this well-known genus of marine shells in the British strata. They are sparingly distributed through the several formations, from the Silurian to the newer Tertiary. One species (Mytilus Lyellii, Wond. p. 405, fig. 2) occurs in the Wealden, associated with fresh-water shells. Of the genus termed Modiola, which comprises those mussels that have a rounded anterior termination, nearly forty British species have been discovered; ranging through the fossiliferous strata, from the Silurian to the Crag. A beautiful species (Modiola elegans. Min. Conch. tab. 9), with the shell generally retaining its pearly coat, is found in the London Clay, and in the limestone of Bognor. An undescribed striated Modiola (which may be named Those species of Modiola, which excavate hollows in stones, and inhabit them, are arranged in a genus termed Lithodomus. The occurrence of these shells in the remaining erect pillars of the Temple of Jupiter Serapis (Wond. p. 106), at Puzzuoli, has afforded important and unequivocal evidence of the physical mutations which that part of Italy has undergone. Two species of Lithodomi have been found, by Mr, Lonsdale, in the Oolite. Pholadomya. Ly. p. 272, fig. 290.—This genus of shells (established by Mr. James De C. Sowerby in the Min. Conch. 1826), comprises about twenty British fossils, all of which, with but two exceptions, occur in the Lias and Oolite. They are equivalved shells, with the posterior end short, and rounded, and the anterior elongated and gaping. The surface is generally marked with ribs, or alternate elevations and depressions, diverging obliquely from the beaks to the margin. In the clay at Osmington and Radipole, near Weymouth, a large species (P. Æqualis, Min. Conch. tab. 546) is abundant. The Oolite of Brora, in Scotland, contains several species. The only species found in our Chalk, is the beautiful shell (P. decussatum), figured Foss. South D. tab. XXV. fig. 3, and first discovered by me, in 1820, in a bed of Chalk Marl, which at that time was exposed at low-water, at the base of the cliff at Brighton, near the present entrance to the Chain-pier. The same species has since been found at Clayton, Hamsey, Southbourne, and other localities of the Marl. FOSSIL PHOLADES. Pholas. Lign. 166, fig. 5, 6.—The common boring bivalve called Pholas, must have attracted the attention of every stroller by the sea-shore, from the numerous perforations in blocks of chalk, and other limestones, occasioned Masses of wood perforated by Pholades, from which all traces of the shells have disappeared, have given rise to some curious fossil remains, which are often very enigmatical to the young collector. In the Kentish Rag, as for example, in Mr. Bensted's quarry, near Maidstone, large blocks of stone are found, covered with groups of subcylindrical mammillary projections, which are obtuse or rounded at the apex. In some examples the interstices between these bodies are free; in others they are occupied by a reddish brown, friable substance, presenting obscure indications of ligneous structure: and rarely, distinct woody fibres may be observed, the direction of which is transverse, or In the White Chalk specimens of this kind are occasionally found. A remarkable fact, relating to some of the specimens from the Iguanodon quarry, remains to be mentioned. Upon breaking off the projections, to ascertain if any traces of the shells of the Pholades remained, we discovered in several, near the apex, a univalve shell, a species of Nerita. Lign. 166, fig. 6, represents a fragment of stone with two of the casts, which have been broken, and in each, at a, a univalve is imbedded. At b, the ligneous structure of the original wood is visible. The only hypothesis that will account for the appearance of these univalves in their present position, is that of supposing that the Nerites crawled into the cavities made in the mass of timber, after the shells of the Pholades had been removed; and that the wood became imbedded in a sand-bank, and the univalves enclosed in the cavities; the ligneous structure in a great measure perished, and the stony casts of the perforations of the borers, with the imprisoned univalves, remained. The Nerites, as shown in the example figured, do not occupy any particular position in the tubes; one has the apex towards the end of the cavity, and the other lies in a transverse direction. TEREDO. Teredo. Ly. p. 24.—It will be convenient to notice in this place another genus of boring shells, whose fossil remains are far more abundant than those of the Pholas. The Teredo navalis, or Ship-worm, which is the most vermiform Trigonia. Lign. 127, fig. 1, 2, 4.—These bivalves are related to the ArcadeÆ and NuculÆ, but distinguished by the peculiar character of the hinge; the right valve has two large oblong teeth, which diverge from the umbo, and are strongly furrowed, and fit into two corresponding grooved cavities, in the opposite, or left valve. These shells are very thick and nacreous; they abound in certain strata of the Oolite and lower Cretaceous formation, but have not been observed in any deposits of this country older than the Lias; there are nearly thirty British species. Two living species of Trigonia (Trigonia margaritacea and T. Jukesii) are known, both inhabitants of the seas of New Holland, where they are associated with TerebratulÆ. Some of the argillaceous beds of the Oolite, as the Oxford and Kimmeridge clays, abound in TrigoniÆ; Osmington and Radipole, near Weymouth, are celebrated localities for these fossil shells, which are found there in great perfection; and on the French coast, where similar strata appear, the TrigoniÆ are equally abundant. Under the cliffs, near Boulogne harbour, the shore is strewn with them. Three common species are figured in Lign. 127. The casts of most of the species are smooth, as in fig. 2; and the collector should, therefore, search for impressions of the outer surface, when the shell is absent, as is generally the case in the Portland Oolite and Shanklin Sand, in which TrigoniÆ are very numerous. Near Highworth, in Wiltshire, very fine and large examples of Trigonia costata, fig. 4, occur, with the shell preserved. The impressions of the large, oblong, diverging teeth of the hinge, are usually so strongly marked in the casts, as to render it easy to identify the shells of this genus. The quarries of the Portland Oolite at Swindon, Wilts, teem with casts of TrigoniÆ, collocated with Ammonites. In the Isle of Portland they are also very numerous, some beds of stone being so friable, from the numerous cavities left by the removal of the substance of the shells, as to be unfit FOSSIL FRESH-WATER BIVALVES. FOSSIL FRESH-WATER BIVALVES. The animals of the shells hitherto described are, with scarcely any exception, inhabitants of the sea; and the marine origin of the strata in which they occur, may consequently be inferred, with but little probability of error. I now propose noticing the fossil remains of those bivalves which inhabit rivers, lakes, streams, and pools of fresh water. The marine, or fresh-water, character of fossil shells, is inferred from their resemblance to the recent mollusca, whose habits are known; for the shells alone present no unequivocal marks, by which even the experienced conchologist can pronounce whether an extinct form belonged to a marine or to a fluviatile mollusk, although certain characters may admit of an approximative inference. Thus, for instance, as none of the known living fresh-water bivalves belong to the previous division, the Monomyaria, the presence in a stratum of numerous shells with but one muscular impression, would afford a fair presumption of the marine origin of such, deposit. The remains with which the shells are associated and the mineralogical characters of the strata in which they occur, would, of course, afford important corroborative evidence. The living fresh-water bivalves comprise but a few genera and species; and those which have been found fossil in the British strata belong to but four or five genera. Their distribution Unio. Ly. p. 28.—The river Mussels, or UnionidÆ, have a solid, pearly shell, with two principal and two lateral teeth on the hinge; and their umbones, or bosses, are generally smooth, or longitudinally undulated. Those which have no cardinal teeth are arranged under the genus Anodon: but it is not necessary for our present purpose, to enter into minute conchological distinctions. In number, variety, and beauty, the species which inhabit the large rivers of North America present a striking contrast with the few and homely British fresh-water mussels; nor have we, in a fossil state, any shells of this family at all comparable with those living types. The earliest undoubted shells of this genus from the British strata, are, I believe, those first discovered by me in the strata of Tilgate Forest, (Foss. South D. p. 45, and Foss. Lign. 131. Unio Valdensis. (1/3 nat.) Wealden; Isle of Wight. In 1844 I discovered a large species in the Wealden at Brook Point. I have named it Unio Valdensis. I shall reserve my remarks upon the important aid these Lign. 132. Cyclas and Melanopsis. Wealden; Sussex. Cyclas. Wond. p. 404. Ly. p. 28.—Another genus of fresh-water bivalves is termed Cyclas, of which there are ten species in the Wealden formation: and, with the exception of four or five recent forms, which occur in the tertiary fresh-water strata, none others have been found in England. FOSSIL PTEROPODA. PTEROPODA. GASTEROPODA. In the Ludlow strata there are found small fragile elongated conical shells without chambers, which are supposed by Professor E. Forbes to be identical with a recent genus of pteropodous mollusca, common in the Mediterranean, called Creseis. They seldom exceed two inches in length. Of another genus, named Conularia, six Species have been discovered in the Silurian formation. Lign. 133. Fossil Shells of Gasteropoda.
FOSSIL SHELLS OF GASTEROPODA. The univalve shells, as we have previously explained, are the calcareous cases, or coverings, of a more highly organized class of molluscous animals, than the inhabitants of the bivalves (see p. 366.), for they possess a head and mouth with jaws, eyes, and feelers; and while the Acephala, with but few exceptions, are incapable of locomotion, the Encephala are almost all of them furnished with organs of progression, and can creep, climb, and swim, or float on the surface of the water. Their shells are for the most part formed of one valve, hence the name of univalve; but in The Gasteropoda generally creep by means of a fleshy disk, or foot, which is situated under the belly. Some kinds are terrestrial, others inhabit trees, many live in rivers and streams, others in stagnant and brackish waters; but the greater number are denizens of the sea. The Common Snail, River Snail, and Periwinkle, are instances of terrestrial, fluviatile, and marine forms. The organs of respiration are situated in the last whorl of the shell; and in some genera the border of the mantle, or integument surrounding the body, is prolonged into a siphon, by which the water is freely admitted, without the head or foot being protruded: in these mollusks the shell has a corresponding channel to receive the siphon, as in the Whelk, or Buccinum, and in the fossil shell Lign. 133, fig. 4. The Gasteropoda are generally provided with an operculum, or movable valve, by which the aperture is closed and defended when the animal retreats within its shell. In some species the operculum is a mere horny pellicle; in others it is a solid calcareous plate of considerable relative thickness. These mollusca, as is but too well known of the terrestrial species, consume large quantities of food. Some are herbivorous, and others carnivorous; many prey on living, and others on decaying animal and vegetable substances. The well known Tiger Cowry (Cyprcea tigris) in its earliest stage has a minute helicoid (snail-like) shell. The various conditions in which the remains of univalve shells occur in the mineral kingdom have already been so fully explained, that but a few additional remarks on that subject are required (see p. 382.). The Gasteropoda are found to progressively diminish in number with the antiquity of the deposits, and it was once supposed that this type of molluscous organization was not contemporaneous with the ancient Cephalopoda. My discovery of several genera associated with Ammonites in the chalk (see Foss. South D. pl. xviii, xix) first tended to invalidate this hypothesis; and the subsequent researches of Dr. Fitton, Professor Phillips, and other geologists have shown that the presence or absence of Gasteropoda in a stratum may generally be ascribed to the circumstance of FOSSIL FRESH-WATER UNIVALVES. Fresh-water Univalves.—The fossil shells of Gasteropoda that are undoubtedly fluviatile, comprise but few genera and species, and are confined to those deposits, which, from the corroborative proofs afforded by other organic remains, are unquestionably of fresh-water origin. Such are the intercalated beds of clay and limestone in the London and Paris basins, the Wealden formation, and certain strata in the Carboniferous system. The most numerous specimens are principally referable to the common fluviatile genera, Paludina, LimnÆa, Planorbis, and Melanopsis (see Ly. p. 29). Paludina. Lign. 133, fig. 1. (Wond. p. 401, Ly. p. 29.)—This common river shell is of a conoidal form, and the whorls of the spire, and the aperture, are rounded. Eleven British species are known. In the tertiary fresh-water beds of Headon Hill, at Alum Bay, PaludinÆ with the shells perfect, and of a dull white colour, are abundant; and also in the limestone at Shalcombe, in the Isle of Wight, in the state of casts. In both these localities the PaludinÆ are associated with other fresh-water shells. But the grand Lign. 134. Polished Slab of Purbeck Marble. LimnÆa. Lign. 133, fig. 2.—Several species of these fresh-water mollusks inhabit our lakes and ponds, and may be known by their pointed spire, elongated oval body, and delicate thin shell: on the inner lip of the aperture there is an oblique fold. Fossil shells of this genus are found with PaludinÆ in the fresh-water tertiary deposits. Headon Hill and other localities in the Isle of Wight abound in these shells; and in the limestone of Calbourn beautiful casts are very numerous. The Paris basin yields several species; and there are six species in the Isle of Wight Tertiary; I have not observed any decided examples in the Wealden. In the sands and clays the shells are well preserved; in the limestones the casts only remain. Shells of another genus of fresh-water spiral univalves, termed Bulimus (Ly. p. 30), are found associated with the above. A large species (B. ellipticus, Min. Conch. tab. 337), occurs in the limestone at Binstead, near Ryde, and at Calbourn; I have collected specimens two inches long from the former locality; they are generally in the state of casts, with a white friable coating of the shell. Planorbis. Ly. p. 29. Wond. p. 400.—The shells of this genus are also numerous in our rivers and lakes, and Melanopsis. Ly. p. 29.—These are spiral univalves, the appearance of which will be better understood by the figures, than by any description. I allude to this genus because a small species is very numerous, with the other fresh-water shells, at Headon Hill; and two or more species are found in the argillaceous strata of the Wealden (see Geol. S. E. p. 249, and Lign. 132). FOSSIL MARINE UNIVALVES. Marine Univalves.—Of the fossil marine Gasteropoda there are no less than eighty genera in the strata of the British Islands, and the species amount to several hundreds. To distinguish the species and genera, reference must, of course, be made to works expressly devoted to fossil conchology, as Sowerby's Mineral Conchology, and Genera of Fossil Shells; or to the works of French authors, particularly those of Lamarck, edited by M. Deshayes, and of M. Blainville. The Penny Cyclopedia contains admirable notices of fossil shells, under the respective heads of the classes, orders, and genera, of the recent Mollusca. Buccinum, of which the common Whelk is an example.—Fusus, Lign. 133, fig. 4. Wond. p. 244.—Pleurotoma, Ly. p. 31. Wond. p. 244.—Cerithium, Lign. 133, fig. 3. Wond. p. 244.—Ancilla, Wond. p. 244. Ly. p. 31.—Voluta, Ly. p. 202, fig. 180.—Murex, Ly. p. 164.—Rostellaria, Ly. p. 201.—To the eight genera here enumerated a very large number of the marine simple univalve shells belong; and they are principally found in Tertiary strata. The animals of these shells are characterized by their respiratory organs, which are formed of one or two pectiniform gills, with a tube or siphon more or less elongated, for the free admission of sea-water to the branchial apparatus. This organization is indicated in the shell, either by a notch, or by a prolonged tubular canal. All the species are, with scarcely any exceptions, inhabitants of the sea, and carnivorous. I have selected for illustration of the genus Fusus, a celebrated shell of the Crag, known among collectors as the "Esssex reversed Whelk," Lign. 133, fig. 4; the spire is twisted in the opposite direction to the usual mode, and the mouth is consequently to the left of the observer; the same species occurs with the spire in the common direction. The shells of the genus Pleurotoma are distinguished by an incision, or notch, in the side of the right or outer lip; and those of Cerithium, by the form of the mouth, see Lign. 133, fig. 3. The latter is a very numerous genus, and more than two hundred fossil species are enumerated; it contains many elegant forms. The Tertiary strata at Grignon are particularly rich in these fossils; the shells are of a pearly whiteness, and as perfect as when recent. Some Cerithia are of considerable size; the C. giganteum is from ten to fourteen inches in length. The genus Potamides comprehends shells closely resembling the Cerithia in form, but which are inhabitants of fresh-water. The Plastic Clay beds at Castle Hill, Newhaven, and in the vicinity of Woolwich, abound in two species of shells, Of the genus Rostellaria, there is a remarkable species in the London Clay, called R. macroptera, from the large wing-like expansion of its outer lip, in adult specimens; see Ly. p. 201. An elegant Rostellaria is found in the Galt, at Folkstone, Casts of a large ventricose, globular univalve, called Dolium, In the Chalk of Touraine, species of the genera Conus (Lign. 135, fig. 1) and Solarium (Lign. 135, fig. 2) are found with the shells preserved. The specimens figured, Lign. 135, are selected to familiarize the student with the difference so commonly observable, between the outer surface of the casts, and that of the shells: in both these fossils the shells are marked externally with lines and Lign. 135. Univalves, from the Chalk of Touraine.—nat.
In the most ancient fossiliferous formations, the Carboniferous; Devonian, and Silurian, many species and genera of Gasteropoda have been discovered. Professor Phillips enumerates more than ninety in the mountain limestone of Yorkshire (Phil. York.), belonging to the genera Turbo, Pleurotomaria, Natica, Euomphalus, Loxonema, Macrocheilus, Platyceras, and Metoptoma. Thirty-four species from the Silurian rocks are figured and described in Murch. Sil. Syst. p. 706. The Natica, Lign. 136, fig. 3, sometimes attains thrice the size represented, and has been found in many localities in England and Ireland. Pleurotomaria. Lign. 136, fig. 4.—This is an extinct genus, distinguished from Trochus by a fissure on the right lip, the position of which is indicated by the band along the Lign. 136. Univalves from the Mountain Limestone.
There are two species of this genus (formerly named Cirrus by Mr. Sowerby) which are of frequent occurrence in the White Chalk of England, in the state of casts, and are figured in my Foss. South D. tab. xviii., under the names of Cirrus perspectivus, and Trochus linearis. The Chalk Marl of Sussex yields in some localities (Hamsey, EUOMPHALUS. Euomphalus. Lign. 137. Murchisonia angulata. Devonian; Eifel. Murchisonia. Lign. 137. An elongated spiral shell, having the outer lip deeply notched, as in the Pleurotomaria (a, Lign. 137). There are upwards of 50 species of this genus, which are characteristic of the palÆozoic rocks. They occur in the Permian, Devonian, and Lower Silurian deposits; the specimen figured is from the Devonian, or Old Red of the Eifel. Chiton. Valves of Chitons have been found in the Magnesian limestone, near Sunderland, by Prof. King, (Permian Fossils, Pal. Soc. p. 202, pl. xvi.), and in the Silurian rocks of Ireland, by Mr. Salter, Geol. Journal, vol. iii. p. 48. SPHÆRULITES. SphÆrulites. Lign. 138. SphÆrulites from the Chalk of France and England.
The species found in the Sussex Chalk, Lign. 138, fig. 2, is characterized by the longitudinal striÆ on the outer surface. In some examples there is an external longitudinal furrow, and a corresponding internal ridge. The SphÆrulites sometimes occur in groups in the Sussex chalk; I had a large water-worn mass, consisting of five or six individuals, anchylosed together. Some beautiful specimens collected by the late Mr. Dixon from the Chalk, near Worthing, are now in the British Museum. MOLLUSKITE. Molluskite; or the carbonized remains of the soft parts of mollusca.—Before proceeding to the consideration of that numerous and important division of the mollusca the Cephalopoda, I will offer a few remarks on a carbonaceous substance resulting from the gelatinous matter of which the soft bodies of these animals are composed, and for which I have proposed the name of molluskite, to indicate its nature and origin. Lign. 139. Coprolites and Molluskite. Chalk and Greensand.
This substance is of a dark brown or black colour, and occurs either in shapeless masses, which are irregularly distributed among the shells and other organic remains, in sandstone, limestone, &c., or as casts of shells, or occupying their cavities, as in the specimen Lign. 139, fig. 3, which is a vertical section of a spiral univalve (Rostellaria), filled with the soft parts of the animal, converted into molluskite. Upon analysis this substance is found to contain a large proportion of animal carbon. "Now nearly the whole of the shells in the beds of Kentish Rag," Mr. Bensted remarks, "have their shells open, as if they were dead before their envelopment in the deposit. And, from the large quantity of water-worn fragments of wood perforated by Pholades imbedded with them, it seems probable that this stratum had originally been a sand-bank covered with drifted wood and shells, thus presenting a very analogous condition to the phenomenon above described." The gelatinous bodies of the TrigoniÆ, OstreÆ, RostellariÆ, TerebratulÆ, &c., detached from their shells, may have been A microscopical examination of the Maidstone molluskite detects, with a low power, innumerable portions of the nacreous laminÆ of shells, intermingled with the carbonaceous matter, many siliceous spicula of Sponges, minute spines of Echinoderms, and fragments of Corals; these extraneous bodies probably became entangled among the floating animal matter. A large proportion of the shelly laminÆ, examined with a high power, displays the peculiar structure of the TerebratulÆ (see Lign. 126, fig. 2a), of which several species are abundant in the Kentish Rag. The dark masses and veins so common in the Sussex and Purbeck marbles are produced by molluskite. If at the period of their envelopment the shells were empty, they became filled either with grey marl and limestone, or with white calcareous spar; but if they enclosed the bodies of the Mollusks, the soft mass was changed into carbonaceous matter; and in polished sections of the marble, the molluskite appears either in black or dark brown spots, or fills up the cavities of the shells. The dark blotches and veins observable in the fine pillars of Purbeck marble in the Temple Church, London, are produced by molluskite; and the most beautiful slabs of Sussex marble owe their appearance to the contrast produced by this black substance in contact with white calcareous spar. Carbon, resulting from animal remains, is of frequent occurrence in many strata; and the fetid emanations from GEOLOGICAL DISTRIBUTION OF SHELLS. Geological Distribution of the Bivalve and Univalve Mollusca.—If the more rare and splendid organic remains may be regarded as the "Medals of Creation," the fossil testaceous mollusca, from their durability, numbers and variety, may be considered as the current coin of Geology. Occurring in the most ancient fossiliferous strata in small numbers, and of peculiar types,—becoming more abundant and varied in the secondary formations,—and increasing prodigiously, both numerically and specifically, in the tertiary, these relics are of inestimable value in the identification of a stratum in distant regions, and in the determination of the relative age of a series of deposits. To the solution of the former problem the sagacity of the late Dr. William Smith first suggested their applicability; Many useful tables have been constructed by Professor Phillips, Silurian System. Ly. p. 350. Orthis orbicularis; Ly. fig. 409. Devonian System. Ly. p. 342. Calceola sandalina; Ly. fig. 403. "The Silurian System," by Sir R. I. Murchison, a splendid work on the rocks and fossils of the above formations, contains numerous figures of the shells peculiar to each group of strata; and many other species are delineated in the Memoir on the Devonian deposits of Devonshire and Cornwall, by Sedgwick and Murchison, Geol. Trans. New Series, vol. v. plates lii-lvii. A Memoir on the PalÆozoic Rocks of Germany and Belgium, by the same distinguished geologists, is also accompanied by many figures of fossil shells belonging to the same geological epochs. Geol. Trans. New Series, vol. vi. See also Prof. M'Coy's "Silurian Fossils of Ireland," and his Description of the British PalÆozoic Fossils in the Woodwardian Museum at Cambridge, in Prof. Sedgwick's "Synopsis of the Classification of the British PalÆozoic Rocks," of which two Parts are already published. Carboniferous System. Ly. 308. Wond. p. 736. Producta punctata; Wond. p. 736. For the shells of the Mountain Limestone, reference should be made to the second vol. of Prof. Phillips's "Geology of Yorkshire;" to Prof. M'Coy's "Carboniferous Limestone Fossils of Ireland;" and to Prof, de Konick's "Anim. Foss. Belg." The fossils of other portions of the Carboniferous System are illustrated in Phillips's "PalÆozoic Fossils of Devon;" Magnesian Limestone and Trias. Ly. p. 301.
Prof. King's elaborate Monograph on the Permian Fossils (published by the PalÆontographical Society) should be consulted by the student. Lias. Ly. p. 273. Pleurotomaria Anglica; Ly. p. 39. Oolite. Ly. p. 257. GryphÆa virgula; Ly. fig. 268. Many of the characteristic shells of the Oolite and Kimmeridge Clay, are figured in Plates XXII. and XXIII. of Dr. Fitton's Memoir on the Strata below the Chalk; Geol. Trans. New Series, vol. iv. The fossil shells of the Great Oolite are figured and described by Messrs. Morris and Lycett, in the Memoirs of the PalÆontographical Society; and valuable Papers on the Brachiopods of the Oolite and Lias, by Mr. Davidson, have been published by the same Society. Wealden and Purbeck. Wond. vol. i. Geol. S. E., Foss. Tilg. For., and Ly. p. 225. Melanopsis; Wond. pp. 401 and 404. The shells of the Wealden are also figured by Dr. Fitton, Geol. Trans. New Series, vol. iv. Pl. XXI. Chalk Formation. I.—Shanklin, or Lower Greensand. Ly. p. 219. Dr. Fitton's Memoir, previously quoted, contains numerous figures of the characteristic shells of this division of the Chalk, particularly of the species which abound in the celebrated Whetstone of Devonshire. Geol. Trans. New Series, vol. iv. Pl. XIII-XVIII. See also Prof. E. Forbes's Catalogue of Lower Greensand Fossils, in the Quart. Geol. Journal, vol. i. II.—Galt and Upper Greensand. Wond. p. 307; Ly. p. 218. Inoceramus concentricus; Wond. p. 330, fig. 1. In Plates XI. and XII. of Dr. Fitton's Memoir, there are figures of more than twenty characteristic shells of this division of the Chalk. III.—White Chalk. Ly. p. 211, Foss. South D., Geol. S. E. Some cretaceous species are delineated in Lign. 125, 126, 128, 129, 130, 138; and Sir C. Lyell figures other species; but I must refer the student to the Foss. South D., Geol. S. E., and Dixon's Fossils of Sussex, as accessible works containing numerous figures of the fossil shells of the Chalk. Accurate descriptions and representations of all the British chalk shells, however, are still much required. Mr. Davidson has done much towards the illustration of our Cretaceous Brachiopods; and the shells of the Cretaceous strata of the United States are figured and described in an elegant work by Dr. Morton, of Philadelphia. Tertiary Formations. I.—Eocene. Ly. p. 174; Wond. p. 226. The specimens figured by Sir C. Lyell have been so carefully selected, and are so well engraven, as to present a coup-d'oeil of the most characteristic shells of the three grand divisions of the Tertiary Deposits. I have reserved for especial mention in this place, the work, which will afford the student of British fossil Conchology the most important aid in the identification of specimens, namely, the "Mineral Conchology of Great Britain," by the late eminent naturalist, Mr. James Sowerby, and continued by his son, Mr. James De Carle Sowerby; in six volumes 8vo., with several hundred coloured plates. Unfortunately, this work has long been discontinued; and the rapid progress of discovery, and the numerous foreign publications on every department of fossil conchology, almost forbid the hope that it will be resumed by the present proprietor. Although the high price of this work places it beyond the reach of many individuals, it will be found in most libraries of Natural History. ON COLLECTING FOSSIL SHELLS. On the Collection and Arrangement of Fossil Shells.—The instructions already given for the collection of corals, echinoderms, &c., will have familiarized the student with the methods generally adopted, and render it unnecessary to enter into much detail. The shells in arenaceous deposits, particularly in those of the Tertiary formations, are commonly so perfect, as merely to require careful removal: those in the clays are more fragile, and must be extracted with great caution; and, when very delicate, should be left attached to the clay or shale. The specimens extracted entire may be kept either in paper trays, lined with wadding, or fixed to pieces of card or thin board covered with paper, by thick gum-water; three or four specimens being attached in different positions, so as to expose the essential characters, as the aperture, spire, and back of the univalves, and the hinge, muscular imprints, &c. of the bivalves. Where only casts remain, search should be made for an impression of the outer surface of the shell, and a cast taken of it in wax, kneaded bread, or plaster of Paris. In indurated clays, sometimes both shells and casts may be obtained; and a specimen Shells imbedded in chalk, limestone, &c., often require much labour to display their more delicate and important characters. For clearing chalk specimens, a stout penknife, and a few gravers or gouges of various sizes, will be necessary; and by a little practice, the spines of the Spondylus (Lign. 128), and the beaks and hinge of Inocerami (Lign. 129), &c., may be readily exposed. A small stiffish brush, used with water, is also serviceable. The shells in compact stone, as those of the mountain limestone, must generally be cleared with the hammer and chisel. Common species may be broken out, and, from several examples, probably one or two will be found perfect; but choice and rare specimens should not be thus risked; they will amply repay the trouble of the less expeditious method of chiselling away the surrounding stone. Casts may be taken in gutta percha, &c. To determine the names of the specimens that he has collected should be the next care of the student. No method will so readily initiate the young collector in fossil conchology, as the careful examination of a small series of the common species, with their names attached. I subjoin a list of some localities of fossil shells, to direct research in places which are likely to be productive. BRITISH LOCALITIES OF FOSSIL SHELLS. BRITISH LOCALITIES OF FOSSIL SHELLS. Aldborough, Suffolk. The usual shells of the Crag. Alum Bay, Isle of Wight. Eocene tertiary; marine and fresh-water shells. Ancliff. Great variety of minute shells of the Oolite. Arundel, Sussex. Chalk-pits in the neighbourhood. Atherfield, Isle of Wight, Shells of the lower beds of the Lower Greensand, in great variety and abundance. Aylesbury, Bucks. Kimmeridge Clay: near Hartwell. Aymestry. Pentamerus, and other Silurian shells. Barnstaple, North Devon. Numerous Devonian shells. Barton Cliff, Hants. Eocene shells in profusion. Bedford. Lower Oolite, TerebratulÆ, OstreÆ, MyadÆ, &c. Binstead, near Ryde, Isle of Wight. Tertiary: in the stone-quarries, terrestrial and fresh-water shells, as Bulimus, Helix, LimncÆ, and Planorbis. Blackdown, near Collumpton, Devon. Greensand. Numerous silicified shells, of great beauty. Trigonia, Venus, Corbula, Rostellaria, &c. &c. Bognor Rocks, Sussex. Eocene Tertiary. Vermetus, Pectunculus, Pinna, Voluta, &c. Bolland. Numerous shells of the Mountain Limestone. Bradford, Wilts. Numerous Oolitic shells. Avicula. Bramerton Hill, near Norwich. Shells of the Norfolk Crag. Brighton. Strondylus, Terebratula, Ostrea, Pecten, Inoceramus, &c. Many species in the chalk. Bromley, Kent. Eocene Tertiary. Oyster conglomerate. Brook-point, Isle of Wight: about one mile east of the Chine. Wealden: Unio valdensis, Cyclades, PaludinÆ, &c. Brora, Scotland. Oolite. Pholadomya, Sanguinolaria, &c. Calbourn, Isle of Wight. Tertiary. Fresh-water Univalves. Cambridge. In the Galt and Chalk-marl, the usual shells. Castle Hill, near Newhaven, Sussex. In the Tertiary strata, on the summit of the hill. Numerous Potamides, Cyclades, and other fresh-water shells, OstreÆ, with pebbles. Chardstock, Devon. The fossils of the Lower Chalk. Cheltenham. Fine shells of the Oolite and Lias. Chute, near Longleat, Wilts. Greensand shells, in abundance. Clayton, near Hurst, Sussex. In Chalk-marl, many rare shells; as, Dolium nodosum (Min. Conch. tab. 326.) Clifton. Carboniferous Limestone. Spirifera, Producta, &c. Coalbrook Dale. Silurian and Carboniferous fossils. Cork. In the vicinity. Carboniferous limestone shells. Crich Hill, Derbyshire. The usual shells of the Mountain Limestone. Cuckfield, Sussex. In the Sandstone and Grit, fresh-water shells of the Wealden. Dudley. Profusion of shells of the Silurian strata. Dundry, near Bristol. Beautiful shells in the Inferior Oolite. Earlstoke, Wilts. Many shells of the Greensand. Faringdon, Berks. The usual shells of the Oolite in the Coral Rag, &c.; and of the Greensand, in the Gravel-pits. Folkstone, Kent. Galt. Inoceramus, Arca, Rostellaria, Dentalium, &c. Lower Greensand, GryphÆa, Ostrea, &c. Gravesend. Beautiful shells of the White Chalk. Hampstead Cliff, Isle of Wight. Fresh-water Tertiary shells. Hampton Quarry, near Bath. Abounds in Oolitic shells. Hartwell, Bucks. On the estate of Dr. Lee, beautiful shells of the Kimmeridge Clay. Harwich Cliff, Essex. The Crag shells. Voluta Lamberti. Hastings, Sussex. Fresh-water shells of the Wealden. Headon Hill, Isle of Wight. Fresh-water Tertiary shells in profusion. Heddington. Oysters in Kimmeridge Clay (Ostrea deltoidea). Perna, Gervillia, Trigonia, &c. Highworth, Wilts. Very fine TrigoniÆ, and other Oolitic, shells, in the stone-quarries. Hollington, near Hastings. Wealden. Fresh-water bivalves, &c. Holywell, near Ipswich. Shells of the Crag, abundantly. Hordwell Cliff, Hants. The usual shells of the Eocene deposits, in immense quantity, variety, and perfection. Horningsham, near Frome, Wilts. Oxford Clay. Terebratula, Pecten, &c. in great numbers. Horsham, Sussex. Fresh-water shells of the Wealden, in the stone-quarries. Humbleton Hill, Sunderland. Permian fossils. Hythe, Kent. Greensand. Trigonia, GryphÆa, Pecten, &c. Ilminster, Somerset. Brachiopoda, &c. Inf. Oolite and Marlstone. Ipswich. The usual Crag shells. Langton Green, near Tunbridge Wells. Wealden. In the sandstone quarries, Uniones, Cyclades, &c. Leckhampton Hill, near Cheltenham. Numerous shells of the Inferior Oolite and Lias. Lewes. Inoceramus, Pecten, and usual shells of the White Chalk and Chalk Marl. Ludlow. Pentamerus, Spirifera, &c. and other Silurian shells. Lyme Regis. Lias. Plagiostoma, GryphÆa, Trochus. Malton. Beautiful shells of the Oolite. Matlock, Derbyshire. The mountain limestone in the vicinity abounds in the characteristic shells LeptÆna, Spirifer, &c. Minchinhampton. Numerous shells of the Great Oolite. Osmington, near Weymouth. Purbeck; fresh-water and marine shells: Oolite; Trigonia, Gervillia, Perna, Pholadomya, and many other genera. Portland, Isle of. Oolite. In the stone-quarries immense numbers of the genera Trigonia, Venus, Ostrea, Pecten, &c. Pluckley, Kent. Lower Greensand. TrigoniÆ, TerebratulÆ, &c. Radipole, near Weymouth. Trigonia, Pholadomya, &c. in Oxford Clay. Sandgate, near Margate. In the Greensand, the usual shells. Scarborough. In the cliffs along the shore, a profusion of Oolitic and Liassic shells. Selbourne, Hants. In the firestone, Ostrea carinata and other characteristic shells. Shalfleet, Isle of Wight. In tertiary fresh-water limestone, shells of various genera, as Bulimus, Helix, Planorbis, &c. Shanklin Chine. Greensand. In the cliffs along the shore, TerebratidÆ, Gryphites, GervilliÆ, and many other shells. Sharnbrook, Bedfordshire. The usual shells of the Cornbrash and Lower Oolite. Sheppey, Isle of. Eocene. London Clay shells, in abundance. South Petherton, Somerset. TerebratulÆ, Pholadomya, OstreÆ, PleurotomariÆ, &c. of the Marlstone. Stamford, Lincolnshire. Lower Oolite. Univalves and bivalves in profusion. Stonesfield, Oxfordshire. TrigoniÆ and other shells of the Lower Oolite. Stubbington Cliff, near Portsmouth. Eocene shells. Swanage. In the quarries in the vicinity, the prevailing fresh-water shells of the Purbeck limestone. Swindon, Wilts. Oolite. The Portland limestone abounds in the usual shells of that deposit. TrigoniÆ, GervilliÆ, &c. Taunton, Somersetshire, (Pickeridge Hill, &c.) Lima, Pecten, and other Liassic shells. Tisbury, Wilts. Beautiful TrigoniÆ, and other shells of the Portland Oolite. Vincent's, St., near Clifton. The rocks abound in the usual shells of the mountain limestone. Walton, Essex. Shells of the Crag, in great variety. Weymouth. The Oxford Clay and other strata in the vicinity contain great variety of fossil shells. Whitecliff Bay, Isle of Wight. Eocene. Marine and fresh-water shells. Worthing. The chalk quarries in the neighbourhood are remarkably prolific in the usual species; and yield SphÆrulites. Note.—A comprehensive list of the localities for Lower PalÆozoic shells, &c. is given by Prof. M'Coy in the second Fasciculus of the "British PalÆozoic Fossils;" and in the little "Stratigraphical List," published by Mr. Tennant, reference is carefully made to the localities for the fossils of every formation. END OF VOL. I. R. CLAY, PRINTER, BREAD STREET HILL. BOHN’S SCIENTIFIC LIBRARY. MANTELL’S MEDALS OF CREATION.VOL. II.
THE Medals of Creation; OR, FIRST LESSONS IN GEOLOGY, AND THE STUDY OF ORGANIC REMAINS. BY GIDEON ALGERNON MANTELL, LL.D. F.R.S. V.P.G.S. PRESIDENT OF THE WEST LONDON MEDICAL SOCIETY, ETC. AUTHOR OF THE WONDERS OF GEOLOGY, ETC. INCLINED STRATA OF MILLSTONE GRIT, CRICH HILL. IN TWO VOLS.—VOL. II. CONTAINING Fossil Cephalopoda, Crustacea, Insects, Fishes Reptiles, Birds, and Mammalia. WITH NOTES OF GEOLOGICAL EXCURSIONS. SECOND EDITION, ENTIRELY REWRITTEN. LONDON: LONDON: DESCRIPTION OF THE FRONTISPIECE OF VOL. II. PLATE II. Illustrative of the mode of developing Fossil Fishes in Chalk. Osmeroides Mantelli: a Fossil Smelt; from the Chalk, Lewes. See page 626. (One-third natural size.)
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
