No. i.] OSTEOLOGY OF PCEBROTHERIUM. 47 



appear. The principal cusps are now pyramidal in shape, so 

 that when worn they exhibit the first step toward the acquisition 

 of the selenodont pattern. The lower molars still retain a trace 

 of the paraconid, the talon has been raised to the height of the 

 anterior triangle, and the hypo- and entoconids have completely 

 separated. Homacodon is evidently very closely allied to Dicho- 

 bune, and may well be identical with it, but in the absence of 

 more complete information it will be best to separate them 

 provisionally. 



The superior dentition of the Uinta genus, Leptotraguhis, is 

 unfortunately not known. The lower molars are distinctly 

 selenodont, but show their connection with the buno-selenodont 

 type of Homacodon by the fact that the inner cusps are thick 

 and conical, not flattened out into thin plates, and the outer 

 crescents are somewhat trihedral in section, and rather angular 

 than curved. The valleys are widely open above, but narrow 

 rapidly below, becoming mere slits after a moderate degree of 

 attrition. External basal pillars appear on some of the molars. 

 The premolars are simple and trenchant, much as in the tragu- 

 lines : the fourth is, however, somewhat more complicated than its 

 predecessors, and consists of a high, acute, and compressed cone, 

 with a small and sharp antero-internal cusp. From the inner 

 side of the apex of the principal cusp there runs downwards and 

 backwards a thin ridge enclosing a very narrow valley ; this ridge 

 appears to represent the deuteroconid. All the teeth of Lepto- 

 traguhis are very brachyodont, and the molars are rather broad 

 in proportion to their antero-posterior extension ; the premolars 

 have but a moderate extension in the same direction. 



In the White River genus Pcebrotherium the dentition is still 

 unreduced ; the canines are small ; the first premolar in each 

 jaw has become isolated by diastemata both in front and behind 

 it, and the inferior one is implanted by a single fang. The 

 other lower premolars are still very simple, but have become 

 greatly elongated antero-posteriorly, and the enlargement of the 

 antero-internal tubercle gives rise to an anterior valley. The 

 inferior molars show a decided advance toward the modern type 

 of structure as compared with those of Lcptotragulus. The 

 inner crescents are much flattened, the outer more curved ; the 

 crown has become narrower and higher, and shows a distinct 

 tendency to assume the hyposodont condition. The upper 



