1873.] 213 



[Cope. 



unite with the maxillaries or join them and the frontals above the orbit 

 at different points from the anterior to the posterior borders. The tem- 

 poral fossae are so extended as to produce an elevated sagittal crest, 

 which is bifurcate behind, each projection continuing along the outer 

 margin of the occipital region as a lateral crest. The tympanic bone is 

 unossified beneath the meatus auditorius externus, which is bounded in 

 front by a strong postglenoid process. Posteriorly it is bounded by a long 

 descending mastoid process of the squamosal bone, nearly closing it 

 below. This is bounded posteriorly by a long and stout paramastoid pro- 

 cess, which is compressed from before backwards and curves backwards 

 and inwards. The foramen magnum has prominent supero-lateral mar- 

 gins which are nearly straight, and unite at a right angle above. 



The dentition is thus : I. f ; C. ± ; P.M. £ M. | ; a considerable dia- 

 stema separates the premolars and the canine. 



In the species studied, the vertebra; are divided as follows : C. 7 ; D. 

 18 ; L. 7 ; S. 5 ; C. ? ; Of the cervicals the seventh only is not pierced by 

 the arterial canal. The atlas has a broad flat "transverse " process. 



The digits are 4—3 ; the third with a symmetrical hoof, those of the 

 exterior digits halved ; the former have two reverted proximal processes, 

 the latter, one. The astragalus exhibits a deeply-grooved and extensive 

 trochlear arc, with rather long neck, which has a greater facet for the 

 astragalus, a lesser for the cuboid bone. 



From the above it is evident that this genus is nearly allied to Tapirus 

 and cannot be removed to another family. Professor Leidy states that 

 the premolars differ from those of Tapir us in having "but one inner lobe 

 connected with the external crest by two transverse crests." The 

 appearance of one lobe is produced by the posterior curvature of the 

 anterior transverse crest round the inner extremity of the posterior 

 crest. 



I now proceed to describe the skeleton more exactly. 



Hyrachyus eximius. Leidy. 

 Hayden's Geol. Survey, Montana, 1871, p. 361. 



Cranium. In the specimen to be described, the anterior portion from 

 the glenoid cavities is wanting. The sagittal crest is quite elevated, and 

 the lateral occipital quite prominent, and continuous below with the 

 superior margin of the squamosal portion of the zygoma. Four nutri- 

 tious foramina pierce the parietal bone near its middle and above the 

 paramastoid process, and two enter the squamosal above the postglenoid 

 process. The paramastoid process approaches near the occipital condyle 

 by its posterior border. I cannot discover the sutural boundaries of the 

 mastoid bone, but that separating the paramastoid process from the 

 process in front of it is distinct. The condyle of the mandible is massive 

 and the posterior border of the latter extends backwards with a slight 

 obliquity. 



