Cope.] 4«)o |Feb.6, 



tlic vessel issuing from tlie postsquamosal, grooves the petrous bone, leav- 

 ing il ut si point Dear that usually occupied by the mastoid foramen. In 

 the second and last genera, and probably in the third, the sinous canal is 

 protected by a bony crest in front, throughout its entire length. 



Aktiodactyla. 



Great diversities are found in this order, especially between the suilline 

 and ruminant divisions. In the former, with the exception of the llippo- 

 potamidte, there are no foramina ; in the Ruminantia they are more nu- 

 merous than in any other order of the class. The Ruminantia are, like the 

 equine Perissodaetyla, characterized by the presence of the supraglenoid 

 foramen ; to this the Camdidm and some others add the mastoid. The 

 Tragulina must be excepted from this rule, for they have nothing but Ihe 

 postglenoid. 



Omnivora. 



Sus, Dicotyles and. Phacocharus ; no foramina. 



Hippopotamus and Ohceropsis ; postglenoid. postsquamosal, mastoid 

 and a rudimental supraglenoid. 



Ruminantia. 



Tragulus ; postglenoid only. 



Oreodon ; postparietal and mastoid. In one specimen of 0. eulbertsoni 

 from Colorado, I find a minute supraglenoid on each side ; in other speci- 

 mens it is wanting. 



Poebrotlterium ; postparietal, postglenoid ; mastoid ; a small supraglen- 

 oid. 



SPC 



Fig. 6.— Skull of Procamrlus occidentalis Leitly, Loup Fork of New Mexico; 

 one-fourth natural size; showing supraglenoid foramen, SPG. 



Procamelus, Oamelus, Auchmia ; postglenoid, supraglenoid and mastoid. 



Bos ; postglenoid and supraglenoid only. 



Antilocapra; postparietal, postglenoid, mastoid, and a large supraglen- 

 oid. 



Giraffa ; pos' glenoid, supraglenoid, postsquamosal and mastoid. 



Ore'ts, Ovis, Vermis; postglenoid, supraglenoid, postsquamosal, postpa- 

 rietal and mastoid, 



