250 



BIOLOGICAL LECTURES. 



conclusion here advocated is founded ; and for that purpose we 

 must first return to the White River selenodonts. One of the 

 most largely represented families in that fauna is the Lepto- 

 merycidae, though the four genera which are associated in it — 

 Leptomeryx, Hypertragulus, Hypisodits, and Protoceras — are so 

 different from one another that much might be said in favor of 

 referring each of them to a separate family. Leptomeryx was 

 a very small animal, the skeleton of which is extraordinarily 

 like that of a traguline, in which group most students of the 

 subject have placed it; but the resemblance is almost certainly 

 a deceptive one, and the real affinities are with the Tylopoda 

 — a conclusion in which I am glad to find myself in complete 

 accord with Dr. Wortman. Of the dentition only the upper 

 incisors are unknown, and at least one of these is present, but the 

 canine has been lost. The lower canine has become an incisor 

 in form and function, while the first lower premolar, though 

 minute, is caniniform, and its shape strongly suggests that in 

 the immediate ancestors of the genus this tooth functioned as 

 a canine. The other premolars are sharp and trenchant, and 

 the molars, as Riitimeyer pointed out, are singularly cameloid 

 in character, though with traguline features also. The skulls 

 hitherto figured and described have all been broken across the 

 very delicate and fragile muzzle, but newly collected specimens 

 show that the skull has a very llama-like aspect and much 

 more nearly resembles that of Poebrothermm than had been 

 supposed. One important difference from the latter should, 

 however, be noted; namely, that the auditory bulla is small 

 and free from cancellous bone. The neck is short, and the 

 cervical vertebrae have none of the tylopodan peculiarities. 

 The fore-limb is much shorter than the hind, as in the tragu- 

 lines, but the individual limb-bones are very like those of 

 Poebrotherium, though the ulna and radius are separate. The 

 forefoot has four digits, the lateral pair very much reduced; 

 the trapezoid and magnum are coossified, as are the cuboid 

 and navicular in the tarsus — both very exceptional features in 

 the family and suborder. The hindfoot has a cannon-bone, of 

 which the distal end is split in the characteristic tylopodan 

 way. The hoofs are slender and pointed. 



