Merriam.] 



Triassic Ichth yopterygia . 



105 



mine the affinities of Cymbospondylus , and through the kindness 

 of Dr. Charles R. Eastman, the type specimens of Leidy's 

 species of Nevada Triassic saurians were obtained for study 

 from the Whitney collection at Harvard University. The 

 type of C. piscosus was not sufficiently well prepared to show the 

 characters of the vertebra', which Leidy apparently did not 

 understand. The matrix was, therefore, removed from the sides 

 of the centra and arches. The form of the vertebrae shows 

 them to belong to the anterior dorsal region. The centra are a 

 little longer than in most Ichthyosauria and are deeply amphi- 

 ccelous, the concave surfaces beginning close to the periphery 

 and sloping sharply the whole way to the centre. There is but 

 one surf ace of articulation for the rib-head. This is situated on 

 a long, broad, and prominent ridge, which begins on the upper 

 side of the centrum and runs downward and forward to the 

 anterior margin. At the superior end it is very broad. It 

 narrows in the middle and widens again at the lower end. The 

 upper portion of the articular surface seems to be continuous 

 with that upon which the upper arch rests. The broad lower end 

 runs to the anterior margin of the centrum. The pedicels of 

 the upper arches are seen to be considerably extended laterally 

 toward the ribs. The spines are moderately high and quite 

 thick, but show no trace of a lateral rib. The zygapophyses are 

 large and strong. They are not brought into the same plane on 

 the right and left sides and are evidently paired. They come 

 nearer to being perpendicular to the long axis of the spine than 

 in Shasiasaurus and the arches are more nearly erect. 



The lateral ridge of the centrum corresponds to the diapophysis. 

 No trace of a parapophysis is present. The diapophysial ridge 

 is divided into a rough upper face and a smoother lower surface 

 by a salient portion situated at the point where the lower end 

 bends forward. The rib articulation was solely upon the 

 diapophysis and principally with the smoother lower surface. 



Measurements of vertebra? of G. piscosus: 



Height of centrum, 4th vertebra 36 rum 



Width " " " 38 



Length " " " 23 



Height of upper arch, 2nd vertebra 49 



Width of spine " " 23 



Thickness of spine " 8J 



