AMERICAN RUMINANT-LIKE MAMMALS. 251 



Hypertragulus is very much like Leptomeryx, and also much 

 like Poebrotherium. It has kept the original shape and func- 

 tion of the canines, which are long and slender. The skull is 

 thoroughly tylopodan in form and proportions and, except for 

 the small and hollow tympanic bulla, greatly resembles that of 

 Poebrotherium. The limbs and feet differ only in a few details 

 from those of Leptomeryx ; for example, the ulna and radius are 

 coossified, but there is no cannon-bone in the hindfoot. 



Hypisodus is the smallest member of the family and was a 

 minute animal. It is remarkable as the most ancient American 

 type with hypsodont molars growing from persistent pulps, and 

 for having apparently ten lower incisors, the canine and first 

 premolar having gone over to that series. So far as it is known, 

 the skeleton is like that of Leptomeryx, though no cannon-bone 

 is formed in the pes. 



Protoceras, the largest genus of the group, equaling in stature 

 the modern musk-deer (Moschus), is also the most curious 

 indeed, one of the most peculiar and bizarre looking of known 

 mammals. The upper incisors have disappeared, but the 

 upper canine, which in the female is small, is in the male a 

 formidable tusk, opposed by the caniniform first lower premolar. 

 The other teeth have resemblances partly to those of Lepto- 

 meryx and partly to those of Poebrotherium. The skull is 

 extraordinary, especially in the male, in which sex there are 

 horn-like protuberances on the parietals and great thickened 

 plates arising from the upper edges of the maxillaries. In 

 both sexes the nasals are extremely short and the narial open- 

 ing exceedingly large, much as in the saiga antelope. The 

 skeleton, limbs, and feet are those of an enlarged Hypertrag- 

 ulus. It may seem to involve a great strain upon credulity to 

 refer Protoceras to the Tylopoda ; yet its relationship to Lepto- 

 meryx and Hypertragulus is perfectly clear, and wherever the 

 latter are placed, the former must accompany them. Wortman 

 is of the same opinion, and in the paper so frequently cited he 

 speaks of "the early Cameloids, Protoceras and Leptomeryx." 1 



One of the most characteristic of American families is the 



1 " The Extinct Camelidae of North America," etc., Bull. Amer. Mus. Nat. 

 Hist., vol. x, p. 100. 



