104 MEMOIRS OF TTTE UNIVERSITY OF CALIFORNIA. 



Skull with narrow rostrum consisting in a large part of prenmxillaries. 

 Facial region relatively shorter than in Ichthyosaurus, and maxillary rela- 

 tively larger. Orbits relatively small, postorbital bar broad, but without lateral 

 temporal opening. Basioceipital with concave condyle. Dentition isodont. 

 Teeth numerous, set in pits in some cases at least. 



Known only from the Middle Triassic of the West Humboldt and New Pass 

 ranges of Nevada. 



Three species of Cymbospondylus, C. pcti-hntx, ('. /j/.sro.sM.v. and C. (jnuidis 

 were described by Leidy from fragmentary vertebrae. 



C. petrinus is represented by forms attaining a length of thirty feet or 

 more. The anterior and posterior faces of the vertebral centra are sharply 

 concave in the central region, but are nearly flat in the peripheral half of 

 the face. The anteroposterior diameter of the dorsal centra is less than one- 

 half of their height. 



The single fragmentary specimen of C. piscosus represents a form smaller 

 than the average of C. pctrinns. The vertebral centra are relatively longer, 

 their anteroposterior diameter equaling more than half of the height. The 

 anterior and posterior faces of the centra are sharply and regularly concave 

 from the periphery to the center of the face. 



C. grandis was founded on a fragment of a caudal vertebra from the West 

 Humboldt Range, and possibly represents a large individual of C. petrinus. 



Fragmentary material recently obtained at New Pass, Nevada, is referred 

 to a new species, C. nevadanus. It is distinguished mainly by the short and 

 massive elements of the epipodial region of the hind limb. 



CYMBOSPONDYLUS PETRINUS Leidy. 



Cymbospondylus petrinus Leidy, Proc. Philad. Acad. Sc., 1868, vol. 20, p. 178. 

 Chonespondylus grandis Leidy, Ibid. 



Cymbospondylus petrinus (Merriam), Univ. Calif. Publ., vol. 3, p. 106. 

 Cymbospondylus? grandis (Merriam), Ibid. 



This species is the best known of the American Triassic ichthyosaurs, being 

 represented by many individuals, which collectively exhibit the greater part 

 of the skeletal structure. It occurs in the exposures of Middle Triassic lime- 

 stones in the West Humboldt Range of Nevada. Closely allied to the typical 

 C. i>etrinus is a form, C. Hcvadanus, which has been obtained in Middle Tri- 

 assic limestones exposed at New Pass, twenty-eight miles west of Austin, 

 Nevada. 



C. petrinus is represented by individuals averaging over twenty feet in 

 length. In one very large skull, no. 9954, which does not seem to be specifi- 

 cally separable from this form, the dimensions of corresponding parts are 



