The base or circumference of the shell is entire; the margin or internal lip is thick and flat. The inner surface is smooth, with the exception of a few irregular projections of nacreous deposit. The hinge is dorsal, the hinge-plate very thick, with a deep fosse beneath the lamellar portion. The cardinal teeth of the right valve are two; the anterior one is the largest, and bifurcated; the lamellar tooth-plate is broad. The anterior muscular imprint is in front of the large cardinal tooth, and immediately behind this impression is the indentation left by the attachment of the retractor muscles of the foot. The posterior muscular imprint is placed at the extremity of the lamellar tooth-plate. The palleal impression extends from one muscular imprint to the other, running parallel with the margin of the base. There is a considerable difference observable in the width of the posterior part of the shell in a series of specimens, which appears to be sexual; for a similar variation occurs in the male and female shells of the recent species from the Ohio.

The collocation of these large mussels with drifted trees and bones of land reptiles, in clays and sands so manifestly of fluviatile origin, completes the analogy between the rafts imbedded in the delta of the Wealden, and those which float down, and become engulfed in the mud and silt of the Mississippi.

FOSSIL CYPRIDES.-The minute crustaceous animals termed Cyprides, of which the shells or cases of several species are so abundant in the Wealden strata, were brought under the notice of the reader in our examination of the tertiary strata at Whitecliff Bay and Headon Hill; and in the clays and shales of Sandown Bay (p. 98). These animals have the body enclosed in a horny case, consisting of two pieces united by a hinge line. They have one compound eye, and four feet, and two straight simple antenna with a tuft of cilia at the extremities. They swim with rapidity, and may be seen actively pursuing the minuter animals on which they prey. Like other crustaceans, they frequently shed their cases, and the surface of the mud spread over the bottom of still lakes is covered

with their exuviæ. The largest living cypris does not exceed one-sixth of an inch in length. In a fossil state these cases appear like minute, white, elliptical, or reniform scales, on the surfaces of the recently separated laminæ of clay, shale, and limestone. After exposure to the weather the cases decompose, and leave the surface of the stone covered with their casts, which appear as minute polished tubercles; some layers of the compact ironstone have a granulated appearance from the abundance of these remains. Three species of the Wealden cyprides are represented in lign. 25.

Fig. 1. Cypris spinigera; the small figure shows the natural size.

2. Cypris granulosa.

3. Cypris Valdensis.

4. Clay, with numerous cases of the species represented fig. 1, of the natural size.

The immense accumulation of the remains of these crustaceans in the Sussex marble is quite surprising; some slabs which I have examined under the microscope, have the shells and their interstices literally crammed with whole and broken cases. As the recent species inhabit either still lakes or gently flowing streams, and not the turbulent waters of estuaries, it follows that sediments

largely charged with the exuvia of cyprides must have been deposited in lakes, or bays, or in tranquil streams, communicating with the flood of waters which transported to their present situation the bones of terrestrial animals and plants. These beds of fluviatile shells and cyprides, with scarcely any intermixture of other organic remains, which are spread over such wide areas of the Wealden formation, afford, therefore, decisive proofs of tranquil subsidence in fresh

water.

FOSSIL FISHES.-But few remains of fishes have been found in the Wealden of the Island; those which have come under my notice are some small teeth, and a fin-bone, of a species of Hybodus (see p. 170); and several teeth and scales of the Lepidotus, a genus of extinct freshwater fishes, with very thick, enamelled, rhomboidal scales, and obtuse hemispherical teeth; the latter are called fishes' eyes by the peasants who collect fossils from these shores.* Detached scales and teeth of two species of Lepidotus occur in most localities of the Wealden deposits. † I found a portion of an intermaxillary bone with several teeth, and a group of ten scales of the Lepidotus Fittoni, in the cliff to the east of Brook Chine.

* Figures of the scales and teeth of one species of Lepidotus of the Wealden are given in "Medals of Creation," p. 438, Pl. VI., fig. 10.

It is rare to meet with any considerable number of scales in contact; but a few specimens were discovered in Tilgate Forest, exhibiting part of the cranium, the opercula of the gills, the pectoral and dorsal fins, and large masses of scales. These are

now in the British Museum, in the room appropriated to fossil fishes.

FOSSIL BONES OF REPTILES.

225

CHAPTER XI.

FOSSIL BONES OF REPTILES-THE IGUANODON-HYLÆOSAURUS

MEGALOSAURUS-CETIOSAURUS-STREPTOSPONDYLUS-PLESIOSAURUS-TURTLES-IMPRINTS ON SANDSTONE

RIPPLE-MARKS

SUMMARY-THE COUNTRY OF THE IGUANODON-VOYAGE ROUND THE ISLE OF WIGHT.

FOSSIL BONES OF REPTILES.-The occurrence of bones and teeth of gigantic terrestrial reptiles in the beds beneath the chalk of the south-east of England, was first announced in the "Fossils of the South Downs," in which many remains of oviparous quadrupeds from the strata of Tilgate Forest are described. Relics of this kind have subsequently been discovered in numerous localities of the Wealden, and nowhere more abundantly than in the Isle of Wight; although search for these highly interesting remains has not hitherto been very actively or judiciously pursued.

The bones are washed out of the cliffs by the inroads of the sea, and strewn on the shore, where they become exposed to the action of the waves, and are soon abraded and deprived of any processes, or other anatomical characters, they may have retained after their original exposure to attrition in the river by which they were transported and imbedded in the strata. Thus those parts which would afford the most valuable information to the anatomist become entirely defaced, and the specimens are for the most part waterworn masses of bone, indicating only the enormous magnitude of the animals to which they belonged. The bones, even when imbedded in the sandstone and sand, are in general abraded, from having been transported by water from a considerable distance; those in the clays are

commonly less injured, from the plastic material with which they were enveloped having, apparently, afforded some protection. The bones are coloured and strongly impregnated with iron; especially those in Brook Bay, which are permeated throughout with pyrites; groups of brilliant crystals of this mineral often invest the outer surface. The medullary cavities are occasionally found lined with white calcareous spar, and the cancellated structure of the bone is often filled with this substance.*

The quantity of bones collected from the seashore in Sandown, Brixton, Brook, and Compton Bays, during the last few years, is very considerable; the examples which I have seen at various times, and in the possession of different persons, must have belonged to between 150 and 200 individuals. And though from their abraded and mutilated condition, but few of the specimens were instructive, yet so large a number proves that the country from which the Wealden deposits were derived, must have teemed with colossal oviparous quadrupeds. Some of the rolled bones indicate more gigantic animals than even the largest from Tilgate Forest, and now in the British Museum.

The Rev. Gerard Smith, in 1825, obtained several fragments of bones of reptiles from Sandown Bay; and in 1829 a considerable number was found by Mr. James Vine, near Bullface Ledge; the latter are now in the collection of the Geological Society of London. In 1834 Mr. John Smith, of Yaverland Farm, collected several large vertebræ of the Iguanodon, portions of two thigh bones, and many fragments of smaller bones: these relics were presented to the Oxford Museum.†

* Some of these osseous boulders and pebbles afford interesting sections for the microscope. Slices from specimens presented to me by the Rev. Charles Pritchard, of Clapham Common, beautifully display the cancellated structure of the bone, with the cells lined with pyrites and calcareous spar.

† See a memoir, by the Rev. Dr. Buckland, on "Bones of the