324 LIAS — SAUEIANS. [Ch. XXI. 



Fig. 417. 



Posterior part of hind fin or paddle of Ichthyosaurus communis. 



Mr. Conybeare was enabled, in 1824, after examining many skeletons 

 nearly perfect, to give an ideal restoration of the osteology of this genus, 

 and of tbat of tbe Plesiosaurus* (See figs. 415, 416.) The latter an- 

 imal had an extremely long neck and small head, with teeth like those 

 of the crocodile, and paddles analogous to those of the Ichthyosaurus, 

 but larger. It is supposed to have lived in shallow seas and estuaries, 

 and to have breathed air like the Ichthyosaur, and our modern cetacea.f 

 Some of the reptiles above mentioned were of formidable dimensions. 

 One specimen of Ichthyosaurus platyodon, from the lias at Lyme, now in 

 the British Museum, must have belonged to an animal more than 24 

 feet in length ; and another of the Plesiosaurus, in the same collection, 

 is 11 feet long. The form of the Ichthyosaurus may have fitted it to 

 cut through the waves like the porpoise ; but it is supposed that the 

 Plesiosaurus, at least the long-necked species (fig. 416), was better 

 suited to fish in shallow creeks and bays defended from heavy breakers. 



In many specimens both of Ichthyosaur and Plesiosaur the bones of the 

 head, neck, and tail are in their natural position, while those of the rest 

 of the skeleton are detached and in confusion. Mr. Stutchburg has 

 suggested that their bodies after death became inflated with gases, and, 

 while the abdominal viscera were decomposing, the bones, though dis- 

 united, were retained within the tough dermal covering as in a bag, until 

 the whole, becoming water-logged, sank to the bottom.^ As they be- 

 longed to individuals of all ages, they are supposed, by Dr. Buckland, 

 to have experienced a violent death ; and the same conclusion might also 

 be drawn from their having escaped the attacks of their own predacious 

 race, or of fishes, found fossil in the same beds. 



For the last twenty years, anatomists have agreed that these extinct 

 saurians must have inhabited the sea ; and it was urged that, as there 

 are now chelonians, like the tortoise, living in freshwater, and others, 



* Geol. Trans. Second Series, vol. i. pL 49. 



f Conybeare and De la Beche, Geol. Trans. 1st Ser. voL v. p. 559 ; and Buck- 

 land, Bridgw. Treatise, p. 203. 



t Quarterly GeoL Journal, to!, ii. p. 411. 



