190 University of California Publications ill Geology [Vol.9 



and the metapodials seem a little more slender, but as nearly as can 

 be determined by comparison of the upper jaw in Cope's specimen with 

 the lower jaw from Nevada, the reduction of the premolars is nearly 

 the same. 



The reduction of the inferior premolars compared with the size 

 of the molars, and especially with that of M 3 , is greater than in any 

 of the other Procamelus forms known to the writer. 



The Nevada form differs from P. robustus Leidy and P. madison- 

 ianus Douglass through its smaller size ; from P. lacustris Douglass 

 through its smaller premolars; from P. ? elrodi through its shorter 

 molar-premolar series, and smaller premolars; from P. fissidcns Cope 

 through its relatively reduced premolars. 



In the cranial fragment represented in specimen no. 19820 (figs. 

 31a to 31c), the rostrum is somewhat higher and in superior view 

 apparently wider than in the skull of P. gracilis figured by Cope. 10 

 The Nevada specimen has been crushed slightly and this may account 

 to some extent for its apparently greater relative width. The narrow 

 nasals are in broad contact with the premaxillaries anteriorly. In 

 the Nevada specimen, the palatal surface between the anterior pre- 

 molars is much narrower relatively than in the specimen described 

 by Cope. 



The mandible (figs. 30a and 30b) does not appear to differ in 

 proportions from that of P. occidentalis and P. robustus. 



In the inferior dentition every element is represented. The wide 

 crown of I. is separated from the canine by a diastema less than one 

 third the length of the diastema between the canine and P x . P 2 has 

 a simple blade-like crown. The root is grooved laterally and may be 

 completely divided at the lower end. P 3 has a blade-like crown with 

 faint incipient folds of the enamel at the anterior and posterior ends 

 of the inner side. The worn crowns of the fourth premolars show 

 a posteroexternal and an anterointernal fold. The crowns are probably 

 in too advanced a stage of wear to show the posterior fold. M 1 is 

 much worn and shows no distinctive characters. In M 2 the posterior 

 lobe is relatively wide transversely. M 3 is uncommonly long antero- 

 posteriorly. Compared with other forms its anteroposterior diameter 

 is very large in relation to the dimensions of the premolars. The 

 posterior lobe of M 3 stands almost parallel with the plane of the first 

 and second lobes, showing a scarcely preceptible bend outward. The 

 medial wall of the posterior lobe is nearly even with the plane of 



10 Op. ext., pis. 76 and 77. 



