424 SAURIAN S OF THE LIAS. [Oh.- XXI. 



ginous rays tliat bifurcate as they approach the edge, like those in the 

 fin of a fish. (See a, fig 458.) It had previously been supposed, says 

 Prof. Owen, that the locomotive organs of the Ichthyosaurus were 

 enveloped, while living, in a smooth integument, like that of the turtle 

 and porpoise, which has no other support than is afforded by the bones 

 and ligaments within ; but it now appears that the fin was much larger, 

 expanding far beyond its osseous framework, and deviating widely in 

 its fish-like rays from the ordinary reptilian type. In fig. 458 the 

 posterior bones, or digital ossicles of the paddle, are seen near 6; and 

 beyond these is the dark carbonized integument of the terminal half 

 of the fin, the outline of which is beautifully defined.* Prof. Owen 

 believes that, besides the fore-paddles, these short and stiff-necked 

 saurians were furnished with a tail-fin without radiating bones, and 

 purely tegumentary, expanding in a vertical direction ; an organ of 

 motion which enabled them to turn their heads rapidly.f 



Mr. Conybeare was enabled, in 1824, after examining many skele- 

 tons nearly perfect, to give an ideal restoration of the osteology of 

 this genus, and of that of the Plesiosaurus.\ (See figs. 456, 457.) 

 The latter animal 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 shal- 

 low seas and estuaries, and to have breathed air like the Ichthyo- 

 saur and our modern cetacea.§ Some of the reptiles above men- 

 tioned were of formidable dimensions. One specimen of Ichthyo- 

 saurus platyodcn, from the lias at Lyme, now in the British Museum, 

 must have belonged to an animal more than 24 feet in length ; and 

 there are species of Plesiosaurus which measure from 18 to 20 feet in 

 length. The form of the Ichthyosaurus may have fitted it to cut 

 through the waves like the porpoise ; but it is supposed that the Plesio- 

 saurus, at least the long-necked species (fig. 457), 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; Stutch- 

 bury has suggested that their bodies after death became inflated with 

 gases, and while the abdominal viscera were decomposing, the bones, 

 though disunited, were retained within the tough dermal covering as 

 in a bag, until the whole, becoming water-logged, sank to the bottom. || 

 As they belonged to individuals of all ages they are supposed, by Dr. 

 Buckland, to have experienced a violent death; and the same con- 

 clusion might also be drawn from their having escaped the attacks 



* Geol. Soc. Transact., Second Series, vol. vi. p. 199, pi. xx. 

 f Ibid., Second Series, vol. v. p. 511. 

 X Ibid., Second Series, vol. i. p. 49. 



§ Conybeare and De la Beche, Geol. Trans., First Series, vol. v. p. 559 ; and 

 Buckland, Bridgew. Treat., p. 203. 

 J Quart. Geol. Journ., vol. ii. p. 411. 



