yielded a few crustacean remains. In the limestone of St. Peter's Mountain, claws of a small kind of crab are frequently discovered (Tab. 57), but no

TAB. 57.-CLAWS OF A CRAB IN LIMESTONE, FROM MAESTRICHT. (Pagurus Faujasii.)

other vestiges of the animal. Faujas St. Fond, and Latreille, have very ingeniously explained this fact, by showing that the claws belonged to a parasitical species, which like the common hermit-crab of our seas, had the body covered by a delicate membrane, the claws alone having a shelly case; hence the latter would be found in a fossil state, while of the other parts of the animal no traces would remain.

26. FISHES OF THE CHALK-SHARKS.-The fossil fishes of the chalk were known only by the teeth, which abound in almost every quarry, until my researches in the chalk-pits around Lewes

brought to light the extraordinary specimens before you, and showed how such delicate remains could be developed. The teeth for the most part belong to fishes allied to the shark; a family which in the ancient, as in the modern seas, appears to have been confined by no geographical limits. Professor Agassiz, by whose genius and perseverance this department of paleontology has been so successfully elucidated, has proposed a classification of fishes, founded upon the peculiar structure of the scales— an arrangement of great utility to the geologist, since the mutilated state in which ichthyolites so frequently occur, render futile the attempt to place them in the existing orders and genera.* *

The teeth of sharks, particularly those of the genus lamna (Tab. 58, figs. 2, 4), are very common in the chalk, and occur occasionally in the flint; they possess a high polish, are in an excellent state of preservation, and are always single, arising from the cartilaginous nature of the jaws of the original. These examples of the recent shark show the number and variety of the teeth in an individual; by the decomposition of the jaw the teeth would be separated and drifted by the water, and therefore, in a fossil state, seldom exhibit any traces of their original position. It may, however, happen, that jaws with teeth will hereafter be discovered, for vertebræ, fin-bones, and even the shagreen skin of sharks, are preserved in some specimens in my collection. The

* See Appendix I.; and Dr. Buckland's Essay, p. 268.

broad rugous teeth (fig. 6) are sometimes found in groups of twenty or thirty; they belong to a fish allied to the shark, in which the mouth was covered

Fig. 1. Notidanus microdon. 2. Lamna Mantellii.

3. Galeus pristodontus. 4. Lamna appendiculata. 5. Ptychodus altior. 6. Ptychodus decurrens.

with these bony processes, like a tessellated paveThe spines, fin-bones, or rays of fishes, also occur in the chalk; and I have one splendid specimen, in which even the tendinous expansion of

the muscle that moved the fin-bone is preserved.* Some of those in my cabinet belong to the same genus as the dog-fish of our coast (spinax acanthias), which has a curved spine in front of the dorsal fin; I place before you a recent and fossil spine, to show their analogy. The mandible, or

TAP. 59.-MANDIBLE OF A SPECIES OF CHIMERA, FROM THE CHALK NEAR LEWES.

(One-half the natural size.)

jaw-bone, of a very curious fish (the chimera) was one of my earliest discoveries in Hamsey marl-pit, and I have since found examples in the chalk of Lewes; other species have been discovered in the green sand of Kent, by Mr. Bensted, and in the Kimmeridge clay, by Sir Philip Egerton.†

The remains of large fishes, belonging to that division called by Agassiz, sauroid, from their com

Fossils of the South Downs, Tab. xxxix.

The nature of these curious relics remained unknown, till Dr. Buckland ascertained that they are the mandibles of several extinct species of chimera.

bining in their structure certain characters of reptiles, have been found in the chalk and green sand of Sussex and Kent. They consist of large, conical, striated teeth, bearing a resemblance to those of crocodiles, with which they were formerly confounded. I have several from the white chalk near Lewes; Mr. Bensted has discovered others in the Kentish rag, and Mr. Rose, in the galt of Cambridge.

27. FOSSIL SALMON, OR SMELT.-But the most remarkable ichthyolites of the chalk, are the fishes belonging to the salmon family (salmonida), and closely related to the smelt (osmerus). Many years since, I succeeded in extricating from the chalk the extraordinary specimen before you.*

The length of the fish is nine inches, and it stands nearly six inches in relief; the back is still attached to the chalk, and the dorsal fin is exposed. There are other examples of the same species in my cabinet, which are almost equally perfect. These ichthyolites were obtained from the quarries in the immediate vicinity of Lewes, during my residence in that town. It is clear that the chalk must have surrounded the fishes while they were alive and in actual progression, and by suddenly consolidating, preserved their forms unaltered; for the body is round and uncompressed, the mouth open, and the

* A beautiful lithograph of this fossil, by Mr. Pollard, forms the frontispiece of the Catalogue of the Mantellian Museum.