250 THE OSTEOLOGY OF THE REPTILES 



tiguous throughout. Two or three epipodials, as broad as long or 

 broader. Ischia long. Large or very large. 



Jurassic. Pliosaiirus Owen, Peloneustes Lydekker, Europe. 



Family Cryptocleididae. Very much Hke the following family, 

 but the neck is shorter, with from thirty-two to forty-four vertebrae; 

 and the coracoids are contiguous throughout. From two to four 

 epipodials, all short. Cervical ribs single-headed. Skull short. 



Jurassic. Cry ptocleidus Seeley, Muraenosaurus Seeley, Tricleidus 

 Andrews, Picrocleidus Andrews, Microcleidus Watson, Sthenaro- 

 saurus Watson, Europe. 



Fig. 174. Skeleton of Trinacromerum osborni, a Cretaceous plesiosaur, as mounted in the 

 University of Kansas Museum. 



Family Elasmosauridae. Head short, neck very long, with from 

 more than fifty to seventy-six vertebrae; ribs single-headed. The 

 scapulae meet in midline; no interclavicular foramen. Coracoids 

 broadly separated on their posterior half. Ischia short. Two epi- 

 podials only, short. 



Upper Cretaceous. Elasmosaurus Cope, Ogmodeirus Williston and 

 Moodie, Leurospondylus Brown, North America. 



Family Polycotylidae. Skull very slender. Premaxillae articu- 

 lating with parietals. Neck not longer than head, with from twenty- 

 three to twenty-six vertebrae; ribs single-headed. The precoracoidal 

 process separates the scapulae in the midline ; an interclavicular fora- 

 men; coracoids contiguous throughout. Ischia elongate. Three or 

 four epipodials, all short. 



Upper Cretaceous. Polycotylus Cope, Trinacromerum Cragin, 

 ? Piratosaurus Leidy, North America. 



