H I P P O T H E R I U M 

 Hippothermm princeps 



THIS species was founded on a right upper molar, represented in plate 

 xix. fig. 12. This specimen in size and extent of folding of the enamel 

 so closely resembles a corresponding tooth of Equiis major that it was at first 

 assigned to that species by Dr. Leidy, the name Hippotlicriitui princeps being 

 applied to it upon Professor Cope pointing out that the anterior inner pillar was 

 free. This is the sole distinction observable between this tooth and a corre- 

 sponding tooth of E. major, while the pillar is, in transverse section, alike in 

 the two, being convex on the outer aspect and concave on the inner free edge, 

 the general appearance being, roughly speaking, heart-shaped. Among the 

 few teeth of E. major in the collection of the United States National Museum 

 is one in which the isthmus connecting the anterior pillar with the adjacent 

 lake is extremely narrow, so narrow in fact as to be almost obsolete. 



In view of this, and considering the great discrepancy in size that prevails 

 between this tooth of H. princeps and those of the other known species of the 

 genus, it would seem best for the present to consider H. princeps a dubious 

 species, and should no other specimens be found, the tooth may be regarded 

 as an abnormal tooth of E. major, showing a reversion in character. 



F. A. L. 



Hippotheriuni gratuni (//. ingemnmi Leidy) 



Is represented by two upper molars, an astragalus, and a single phalanx. 



One of the molars is from a young individual and quite unworn, the 

 upper part of the tooth tapering inward. The other molar, plate xix. fig. lo, is 

 from an animal of moderate age, and shows the enamel folds very prettily. 

 The anterior internal pillar is, in cross-section, a pretty regular ellipse, and is 

 situated opposite the centre of the tooth. The posterior inner pillar is, in the 

 present state of the tooth at least, poorly defined, being marked off from the 



4 49 



