248 



DOUGLASS — FOSSIL MAMMALIA 



The mandible is somewhat smaller than that of S. panms of the Loup Fork of New 

 Mexico. It is less robust, not being so deep or thick. The masseteric area does not extend 

 so far forward. There is some difference in the enamel pattern of the teeth, but just how 

 much is due to wear I cannot say. That of the premolar in the present species is more 

 complex, being crenulate or minutely folded on the inner hikes and inflections. This 

 tooth is smaller especially at the top, but much wear would bring this surface nearer to 

 the area of that of S. panms. The two anterior molars are broader and longer. The 

 teeth do not appear so high from the outside, but are higher above the alveolar border on 

 the inside. The outer enamel inflections do not extend so far down on the outside of the 

 teeth, are more open and incline more forward and the outer lobes arc more angulate. 

 There are small extra enamel islets en M T and M ? . There is no sharp antero-internal 

 angle on the premolar. These comparisons are made with No. 10575 of the Princeton 

 collection labeled Castor panms, Camp creek, Oregon, which evidently does not differ 

 at all from Cope's type from New Mexico (1877, p. 207, PI. LXIX, Figs. 4 and 5). 



In none of the teeth are the principal inner and outer enamel inflections converted 

 into lakes. 



At its preserved stage of wear the grinding surface of I\ has three divisions, an 

 anterior outer, an anterior inner and. a posterior. The anterior outer division is three- 

 lobed, or is a crescent with a long limb extending inward and somewhat backward from 

 near the posterior horn. The anterior horn is at the antero-external angle of the tooth. 

 From this the crescent sweeps backward and inward, the outer border forming the outer 

 margin of this part of the premolar. The inner limb extends transversely inward to the 

 inner border. The anterior inner crescent of the tooth begins near the anterior border of 

 the preceding one, the outer margin forming the anterior and anterior inner border of the 

 tooth. On the posterior part of this crescent near the antero-external horn is a rounded 

 lobe. Much wear would make the two anterior crescents confluent. The posterior part 

 of the tooth is a transverse, pointed oval with the smaller end outward and slightly 

 deflected forward. Its enamel lake has nearly the same form but with sinuous margin 

 Much wear would perhaps make the enamel pattern nearer like that of S. panms. 



The enamel folds and lakes are inclined to be more curved and the enamel borders 

 more sinuous than in S. panms. There is an extra islet in the two anterior molars. In 

 M T it is posterior to the anterior lake and in M 2 - it is anterior. 



The anterior surface of the incisors is more convex than in the bearer, Castor cana- 

 densis, and the antero-posterior diameter is proportionally greater. 



Measurements. 



Length of molar-premolar series 017 



Length of Pj at base 005 



