COXDYLAETHRA. 433 



A cast of the cranial cavity gives the following as the general charac- 

 ters of the brain. The cerebral hemispheres are remarkably small, each 

 one being less by one quarter than the cerebellum. They are sejDarated 

 from the latter and from the large olfactory lobes by strong constrictions. 

 The posterior one is occupied by a thick tentorium. In like manner a wide 

 groove for a robust falx separates the hemispheres above. A notch repre- 

 sents the Sylvian fissure, and the lobus hippocampi is quite large. The 

 vermis of the cerebellum is quite distinct, and the lateral lobes are large. 

 They are impressed laterally by the petrous bones, as in various ruminants. 

 The anterior columns of the medulla are not visible. There are traces of 

 the convolutions on the hemispheres. 



I refer nine species to this genus. Of these only two, P. primcefvus 

 and P. vortmani, are sufficiently well known to render the generic reference 

 certain. The others are mostly known from teeth, and it is highly probable 

 that most of them belong to the genus. They are all from either the Puerco 

 or Wasatch formations — three from the former and six from the latter. 



Species which are known from mandibular teeth may be distinguished 

 as follows : 



Large ; true molars .041 ; Pm. iv .014 ; depth of ramus at M. ii, .027 P. jyHmceviis. 



Medium ; true molars .027 ; depth at M. ii, .017 ; last molar smaller . . . . P. vortmani. 

 Like the last, but the superior true molars without median external marginal tubercle. 



P. puercensis. 

 Length of true molars .0258 ; some of the ijremolars with flat expanded heels. 



P. calceolatws. 

 Smaller ; true molars .022 ; depth at M. ii, .013 ; last molar elongate .P. macropternus. 

 Smaller ; last four molars .027 ; Pm. iv, .007 ; depth at M. ii, .013 ; last molar with short 



heel P. hracliyptemus. 



Smallest; true molars .017; depth atM. ii, .012 ; heel long; cusps elevated. P. ^wMieMSis. 



Besides these, the P. nunienus is founded on some bones without teeth, 

 and the P. heniicomts on superior molar teeth only. The P. sulcatus of the 

 Report of Capt. G. M. Wheeler, Vol. IV (1877), probably belongs to some 

 other genus. 



28 C 



