[CHTHYOPIERTGIA. 



181 



in Ichthyosaurus, more variable in size and in the degree of folding of 

 their wall, and are sometimes enclosed in completed sockets. The verte- 

 bral centra resemble those of Ichthyosauri^ but their neural arches are 

 relatively stouter and articulated to each other by distinctly paired 

 zygapophysial facettes. The anterior paddle is known to be typically 

 Ichthyopterygian in most respects, but the radius and ulna are longer 

 than broad, not closely apposed but separated by a vacuity throughout 

 their length. The typical species is Mivosuurus cornaliamts, known by 

 imperfect skeletons varying from half a metre to a metre in length, from 

 the Trias of Besano, Lombardy. Detached vertebral centra and neural 



FIG. 112. 



Ichthyosaurus quadrisclssus ; fossilized skeleton (A) and outline restoration (B), 

 showing outline of integument with dorsal and caudal fins, one-tenth nat. 

 size. L. Jurassic (U. Lias); Wiirtemberg. (After E. Fraas.) 



arches, fragments of jaws, and a hurnerus from the Muschelkalk of 

 Wiirtemberg are ascribed to M. atavus. Vertebrae, ribs, and portions 

 of jaws of M. nordenskjb'ldi have been obtained from the Trias of Spitz- 

 bergen. The so-called Skutatavmt pacificus, founded on vertebra; and 

 a coracoid from the Upper Trias of Shasta County, California, may also 

 belong to the same genus. 



Ichthyosaurus (figs. Ill, 112, 113 A). In the jaws of Ichthyosaurus 

 the teeth are conical and uniform in character, with a very large im- 

 planted base, which in some species is much thickened by an enveloping 



