HYRACHYUS. 677 



molars are uninterrupted and regular. There is no tubercle between them, 

 and the ridge from the external wall is not prominent. The anterior cingular 

 cusp is low and is in contact with the base of the much higher anterior lobe. 

 The second external lobe of the first true molar has a short vertical ridge 

 near its apex. This ridge is almost as well developed as the anterior ridge 

 on the premolars. 



The inferior molars are distinguished for the width of the anterior 

 basal cingulum, and the large anteroposterior diameter of the second and 

 third premolars. The diastema is also very short, measuring only three- 

 fifths the length of the bases of the first three premolars, while it equals 

 the latter measurement in the H. agrarius. The canine tooth is not much 

 larger than the third incisor, is implanted close to it, and has an antero- 

 superior direction. 



The mandibular ramus is not deep, and the symphysis is narrowed, 

 strongly convex, and rather slK)rt. The infraorbital foramen opens above 

 the posterior part of the third superior premolar. The orbit is entirely 

 lateral, and its anteroposterior diameter is a little greater than its vertical. 

 The superciliary border is rather thick, is somewhat prominent. There is no 

 postorbital process, but the superciliary border curves round and passes with 

 a trace of an angle into the anterior border of the temporal fossa, which for 

 a short distance is transverse. The temporal ridges are weak in their ante- 

 rior parts. The skull is broken off before their union into a sagittal crest. 



Measurements. 



M. 



Length of superior molar series — 0.085 



Length of true molars 046 



Length of penultimate 015 



Width of penultimate 019 



Length of inferior molar series 078 



Length of inferior true molars 047 



Length of penultimate 017 



Width of penultimate Oil 



Width of last premolar 008 



Length of last premolar 012 



Depth of ramus at last premolar 0235 



Length of diastema 019 



Length of bases of three incisors 018 



From the Bridgfer Eocene of the Washakie Basin near South Bitter 

 ■Oreek, Wyoming: 



