10 MEMOIKS OF THE UNIVERSITY OF CALIFORNIA. 



In 1 873 Hulke described the first ich thy osaurian remains known from Spitz- 

 bergen, referring them to Ichthyosaurus, of which two species, I. polaris and 7. 

 nordenskioldti were described. It is apparent from Hulke 's description that 

 the single-headed character of the ribs in the dorsal region was recognized, but 

 no special value was assigned to it. The same material was worked over again 

 by Dames in 1895, and assigned to the genus Mi-roMturtis. Curiously enough, 

 Dames failed to accept the statement that single-headed ribs of this character 

 occurred in Shastasaurus, and assumed that the ribs must be double-headed as 

 in Mixosa-urus, of which he appears to have had little available information. 



In 1873 Sauvage described from the Rhaetic of Saone-et-Loire in France two 

 types of vertebrae designated as Ichthyosaurus rheticns and 7. cnrinatus. In 

 1876 these species were figured and more fully described by Sauvage, there be- 

 ing, however, only fragmentary material available. In the same publication, 

 Sauvage described under the name Rachitrema pellati a form represented by 

 a vertebral arch, a scapula, and several fragmentary arch and limb bones. 

 R/icl/ih'riini was referred by Sauvage to the Dinosauria, but was later referred 

 to the Ichthyosauria. 



The description of a Triassic ichthyosaurian species, Ichthyosaurus cornal- 

 ianus, from the bituminous shales of Besano in northern Italy, by Bassani in 

 1886, marked the beginning of the first studies of the forms in which sufficient 

 material was available for satisfactory investigation of the skeletal characters. 



In 1887, shortly after the description of the Besano specimen by Bassani, 

 Baur (1877, 1) published his brief but important note on the structure of the 

 limbs of the Italian specimens. It was then for the first time clearly shown that 

 the ichthyosaurian limb in the Triassic stage of development was much farther 

 away from the fish type than were the limbs of the succeeding Jurassic forms. 

 The form of the limb elements was somewhat exaggerated in Baur's figures, 

 and his suggestion concerning the origin of the outer element in the mesopodial 

 region in the limb of Baptanodon is perhaps overstated, but his fundamental 

 theory was correct. Baur set aside the Triassic ichthyosaurs with elongated 

 epipodial elements separated by a cleft as a distinct genus, Mixosaurus, and 

 divided the Ichthyosauria into three families; the MIXOSAURIDAE with elon- 

 gated and separated epipodial bones and differentiated dentition ; the ICHTHY- 

 OSATJRIDAE with short epipodials which touch each other, and numerous teeth of 

 nearly uniform shape ; the BAPTANODONTIDAK with three epipodial elements, and 

 no teeth. 



In 1891 Fraas described and figured several jaw fragments, a humerus, and 

 a number of vertebrae from the Wellendolomit of South Germany, referring all 

 of these specimens to Mixosaurus atavus (Quenstedt). Attention was called to 

 the contrast between the depressed crowns of the posterior teeth and the slen- 

 der conical crowns of those farther forward in the jaw. The insertion of the 



