52 SCOTT. [Vol. V. 



which resembles the former in the character of its dentition, but 

 has lost one premolar, the second, in the lower jaw. " The 

 canine and first premolar are especially short, and separated by 

 a very short diastema ; that separating the first and third pre- 

 molars is also short, being less than that which separates the 

 first and second in Procamelus occidcntalis" (Cope, No. 6, p. 



344)- 



In the Pliocene beds occur the highly specialized genera 



Holomeniscus and Escliatins, Cope. In these the reduction of the 

 premolars has reached its maximum, there being but one left in 

 each series. In the former genus the fourth superior premolar 

 is of the ordinary pattern, composed of an external and an inter- 

 nal crescent, while in EscJiatius this tooth is reduced to a simple 

 cone. 



In the existing genera the changes in the dentition are chiefly 

 confined to the increased size and trenchant shape of the exter- 

 nal upper incisors and canines, and the reduction in number and 

 size of the premolars ; in Camelas the number is f, and the first 

 superior premolar is a large caniniform tooth. In AucJicnia 

 this tooth is lost, and the premolars reduced to \ ; the molars 

 are prismatic, though by no means to the same degree as in the 

 Cavicornia, and the anterior and median buttresses of the upper 

 ones much more strongly developed. In AucJicnia there are 

 strong transverse "compression folds" on the anterior walls of 

 the lower molars. 



The milk dentition is not known in any of the older genera of 

 the series. In PcebrotJicriam it agrees essentially with that of 

 the tragulines and the more ancient selenodonts generally. The 

 last upper milk molar resembles a true molar in form and con- 

 struction. D. 3 is composed of a posterior pair of crescents and 

 a long anterior blade consisting of two imperfectly separated ex- 

 ternal cusps and but the rudiment of an internal cusp. D. I and 2 

 resemble the corresponding teeth in the permanent series, if, 

 indeed, the first one changes at all. In the lower jaw D. i 

 appears to change, at least sometimes, for in some specimens it 

 is implanted by two fangs, whereas pm. i has but a single root ; 

 in other specimens the first tooth in the temporary series is like 

 that in the permanent set. D. 2 and 3 are not different in any 

 important respect from pm. 2 and 3. D. 4 has the constitution 

 usual among the selenodonts, consisting of three pairs of cres- 



