53 



haps, in the greater relative size of the posterior lobes, and 

 in the more complete closing of the median valley by the 

 junction of the two lobes externally. The ridge which curves 

 downwards and inwards from the external point of the an- 

 terior lobe is unusually well developed, and curves across the 

 entire crown. The cingulum is feebly shown ; it appears on 

 the anterior and posterior ends of the tooth (first molar) and 

 for a very short distance on the outside of the tooth opposite 

 the median valley ; there is no trace of it on the inner side. 



Measurements. 



M. 



Length of entire molar series (about) -080 



Length of premolar series 033 



Length of true molar series (about) -047 



Fore-and-aft diameter of fang of canine -008 



Distance between canine alveoli -009 



Length of diastema 115 



Length of the first molar -015 



Breadth of the first molar -oio 



Depth of ramus below last molar 0245 



Depth of ramus below last premolar -0215 



Greatest thickness of ramus -017 



Length of symphysis (about) 030 



Found at Henry's Fork. 



HYRACHYUS ? 



There are three premolars of the upper jaw which we 

 cannot refer to any known species ; but they are too imperfect 

 to justify the formation of a new species for their reception. 



What appears to be a first premolar is inserted by a single 

 broad fang ; it is too much worn to show the characteristic 

 enamel folding, and is peculiarly broad and short. The second 

 premolar shows the usual foldings of Hyrachyus ; save that 

 a distinct valley enters the tooth from the posterior edge, 

 running forward to the transverse crest, and inclosed by the 

 curving backwards of the internal cone. The crown is nearly 

 square ; the basal ridge is scarcely marked at all. 



Measurements. 



M. 



Length of fifst premolar -on 



Breadth of first premolar -016 



Length of second premolar -012 



Breadth of second premolar -014 



