340 NATURAL HISTORY. 



eye could collect the feeblest rays of light when chasing prey under water. They appear to have 

 beached themselves occasionally on shore, but they could not walk. Professor H. G. Seeley, F.R.S., 

 has shown, by good evidence, that they were viviparous. They do not appear to have bred in the 

 American seas of the age. There were many species of the genus Ichthyosaurus, and they have the 

 nostrils high up in the snout near the orbits, and their opening in the palate was behind the long 

 palate bones. 



Professor O. C. Marsh has founded a new order of extinct reptiles, the Sauranodontia, from 

 specimens obtained in the Jurassic strata of the Rocky Mountains. They were apparently 

 Ichthyosaurs which had no teeth, the jaws being even destitute of a groove for holding them. All 

 the other peculiarities of the Ichthyosaurs (which have, as yet, not been found in America) are 

 present, and their length was from eight to nine feet. 



ORDER PLESIOSAURIA. 



A most extraordinary group of marine reptiles lived during the Secondary ages of the world, and 

 the first skeleton discovered, and which belonged to a kind which flourished in the days of the Lias, 

 excited much attention. It had a very small head like a Lizard, a neck extremely long and snake- 



SKELETON OP PLESIOSAURUS. 



like, a plump body, and a distinct and shortish tapering tail. The limbs were short, the hinder pair 

 being the longer, and they were furnished with paddles, differing somewhat from those of 

 Ichthyosaurus. Dr. Buckland compared it to a Turtle with a Snake drawn nearly through it. The 

 Plesiosaur, as it was called, swam probably on the surface, and fed like a Swan, but most likely on fish 

 and small reptiles. It had no scales, but probably a smooth skin. There were no fins ; and the teeth, 

 as seen in the preserved fossil skulls, are sharp- pointed, curved backwards, and each is placed in a 

 distinct socket, but it does not unite to the jaw by a bony union. The snout tapers, and is flattish, 

 and the orbits are large, but the eye had no sclerotic plates. The outer nostrils open just before the 

 eyes, and the premaxillary bones, usually small in reptiles, are large, and form a large portion of the 

 snout. The inner nostrils appear to be in front of the palate bones, and are separated by the vomers. 

 The head, not much more than one-twelfth part of the length of the body, moved readily by a large 

 condyle on the very movable neck, which has in some kinds more than forty vertebrae. These are 

 faintly biconcave, and the neural arch is not united by bony union. Some ribs, not unlike those of the 

 Crocodile, exist near the root of the neck, and in the body there are transverse processes with curved 

 ribs jointed to them. There are from twenty to twenty-five back vertebrae, and two sacral, whose ribs 

 are broad for the attachment of the ilium. Thirty or forty tail vertebrae succeed, and they have 

 chevron bones. There are thus ribs to the vertebrae, and there are none to the sternum, and this is 

 compensated by a system of ossifications in the walls of the abdomen, arranged in cross rows, each 

 consisting of a middle bone slightly bent on itself, and of six others, three on each side, their pointed 

 ends overlapping. The arrangement of the bones of the shoulder and chest is very remarkable. The 

 sternum is small and band-like, its place being occupied, as it were, by two great coracoids. The 

 blade-bones, small and long, differ from those of any other reptile, and there is an epicoracoid. No 

 clavicles exist, but in some kinds that lived during the Trias they are found. The fore limb ends 

 in five digits, composed of metacarpals and phalanges constricted in the middle, which are numerous 

 in the middle digits. The pelvis is large, to fit the corresponding large limb, and all the bones 

 are present. The femur much resembles the humerus, and the toes those of the fore limb. 



