TRANSACTIONS OF WAGNER 

 16 



WHITE RIVER SELENODONTS 



that it once functioned as a canine, but has dwindled because of the loss of 

 the upper tooth which it opposed. The other premolars increase successively 

 in size and complexity backward ; they are long, low, trenchant, and acutely 

 pointed, with sharp basal cusps ; P3- (and more distinctly p^) has an internal 

 ridge, which incloses a fossette. The lower molars have narrow, compressed 

 crowns, and display the traguline character of ridges upon the anterior cres- 

 cents. Indeed, the entire dentition bears considerable resemblance to that of 

 the tragulines. 



The skull (Plate I., fig. 1) is very much more like that of Poebrotherium 

 and the typical Tylopoda than the mutilated specimens hitherto figured would 

 lead one to suppose ; it has the same elongate, triangular shape, and the same 

 veiy long, slender, and tapering muzzle. It is really surprising to see how the 

 whole character and appearance of the skull are changed, and how its tragu- 

 line resemblances are removed by the addition of the muzzle. While the skull 

 of Leptomeryx is in general very much like that of a minute Poebrotherium, 

 yet there are many noteworthy differences. The orbit is placed much farther 

 forward, its anterior border being over m J ; the zygomatic arch is relatively 

 stouter, and the glenoid cavity presents a curiously notched appearance when 

 seen from the side; the auditory bulla is small and is not filled with cancellous 

 bone, but simple and hollow, and is provided with a long, tubular meatus ; 

 a small facial vacuity is present between the lachrymal, frontal, nasal, and max- 

 illary. The horizontal ramus of the mandible is very slender and the angle 

 is very broad, extending much behind the condyle, but does not form the 

 great, hook-like process which occurs in Poebrotliermm ; the masseteric fossa 

 occupies a very elevated position upon the ascending ramus of the jaw. 



In addition to these obvious and striking differences in skull-structure 

 between the two genera, there are numbers of minor discrepancies which it is 

 not necessary to point out. 



The neck in Leptomeryx is short, and the odontoid process of the axis is 

 peg-shaped. The other cervicals are of the normal artiodactyl type, not like 

 those of the Camclidce. The back is much curved, owing to the elongation 

 of the hind-limbs. 



The fore-limb is short and lightly constructed. The scapula is broad and 

 triangular, and ruminant rather than tylopodan in shape, though not unlike 

 that of Poebrotherium. The humerus has no very definite characteristic, and 

 while quite like that of Poebrotherium, its small size gives it a traguline appear- 

 ance. The ulna is reduced and very slender, but uninterrupted and entirely 



