10 OPTHALMOSAURU8 PLEYDELLI. 



idgcan Cimoliosaurus trochanterius, Owen, Plesiosaurus manseli, 

 Hulke, and the Portlandian Cimoliosaurus portlandicus (Pliosaurus 

 portlandicus), Owen, Baptanodon (Sauranodon) from the Upper 

 Jurassic of North America. In all these species the humerus 

 articulates distally with three bones, corresponding with the ulna, 

 radius, and pisiform, giving the limb a great width. In the Oxford 

 Clay and Kimmeridge species these facets are very unequal in size, 

 but nearly equal in 0. Cantabrigiensis of the Cambridge Greensand. 



The name Ichthyosaurus * was selected by Koenig in consequence 

 of the similarity of the vertebral column to that of the fish, each 

 centrum being exceedingly concave, pliable, and adapted for 

 pelagic life. Opthalmosaurus t was chosen by Professor Seeley to 

 designate his new genus, from the sclerotic plates of the eye 

 already referred to, and which are persistent without exception 

 throughout the whole Order of Ichthyopterygia. Complete skeletons 

 of small Icythyosaurs have been found within the thoracic and 

 abdominal cavity of larger individuals of the same species. These 

 entombed specimens led Professor Seeley to think that some 

 Ichthyosaurs were viviparous, especially as their heads were turned 

 towards the tail of the enclosing animal, but this is not always the 

 case, as Professor Merian described a specimen from the Upper Lias 

 of Wiirtemburg in which the included Ichthyosaur lay with its 

 head towards that of the enveloping specimen. The Ichthyosaurian 

 coprolite is an oval body, measuring usually from 2in. to 4in., and 

 shows the spirally convoluted surface of the intestines. The jaws 

 of the Order are powerful and capacious ; some species were armed 

 with no less than 180 teeth, not fixed in distinct sockets, but in a 

 common alveolar groove. A fracture is usually found at about a 

 fourth of its length from the extremity, which has led to the 

 supposition that these reptiles were furnished with a caudal-fin like 

 that of the cetacea, only instead of being vertical it was horizontal. 

 After the close of the Liassic period there was a tendency on the 

 part of some of the members of the reptilian family to differentiate, 

 as in the shoulder-girdle of Cimoliosaurus ; whose structural 



* IxOvs, a fish ; aavpos, a lizard. t <ty0aA/xbj, an eye ; vavpos, a lizard. 



