GEOLOGICAL SURVEY OF THE TERKITOEIES. 595 



LopJiiodon, Cuvier. Loicer jaw : Third molar with three cross-crests ; 

 premolars three, jSTos. 2 and 3 with longitudinal crests. Upper jaw : Pre- 

 molars with longitudinal crest only, Xo. 4 with two transverse crests. 

 Upper jaw : Premolars with only one transverse crest. 



In Ryracliyus the nasal bones are elongate, and unite with the maxil- 

 laries anterior to the orbit ; in K. eximius above the foramen infra-orditale 

 exterius ; in Tapirus those bones are much shortened, and either do not 

 unite vrith the masillaries or join them and the froutals above the orbit 

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

 poral fossse 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 auditor ius extermcs, 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 

 process, which is compressed from before backward and curves back- 

 ward and inward. The foramen magnum has prominent supero-lateral 

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



The dentition is thus: I. f; 0. i ; P. M. f ; M. f 5 a considerable dia- 

 stema separates the premolars and the canine. 



In the species studied, the vertebrse are divided as follows : C 7 ; T>, 

 18 ; L. 7 ; S. 5 ; 0. (?). Of the cervicals the seventh only is not pierced 

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



The digits are 4 — 3 ; the thi,rd 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. 



Prom the above it is evident that this genus is nearly allied to Tapi- 

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

 that the premolars differ from those of Tapirus in having " but one in- 

 ner lobe connected with the exteral 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 peinceps, Marsh. 



Amer. Jour. Sci. and Arts, 1872, p. 125. 

 From South Bitter Creek. 



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 zj^goma. Four nutri- 

 tious foramina i)ierce 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 condvle of the mandible is mas- 



