OF THE WHITE KIVER BEDS OF MONTANA. 249 



M. 



Width of P T at base 0045 



Length of M T ' 004 



Width of M T 0045 



Length, of M 2 004 



Width of M z 0042 



Length of My 004 



Width of M T 0036 



Depth of ramus under middle of P, c 012 



Depth of ramus under posterior of M T 011 



Steneqfiber complexus, sp. nov. 



The type of this species is part of a skull and mandible with complete dentition (No. 

 42). It was found in a gray sandy layer in a ravine cutting through high bluffs of sup- 

 posed White River age on the west side of the Madison river, in the Lower Madison 

 valley, about nine or ten miles south of Three Forks. As this specimen and some limb 

 bones of a rhinoceros-like animal are the only fossils of importance obtained here, and 

 as the exact relations with the lower White River fossil-bearing beds northwest of Three 

 Forks, about fourteen miles distant, have not been made out, it is impossible to say to just 

 what horizon these beds belong. 



Th is is a young individual. Only one premolar — the right upper one — has been shed. 

 All of the molars are fully protruded and considerably worn. The upper permanent 

 premolars are farther advanced than the lower, which evidently had only begun to grow. 



This species seems to be nearest like Cope's S. (Castor) penimulatus (1883, p. 840, 

 Fl. LXIII, Figs. 18-21). The skull is damaged, yet some points of interest can be made 

 out. There is a marked difference in the mandibles of the two species. In the present 

 one the masseteric area- does not extend so far forward, the anterior margin of the'eoro- 

 noid process rises opposite the back part of the third cheek tooth (M-j), and is nearer to 

 the molars. This process has an entirely different form in the present species. It is 

 high ; (lie anterior border is straight and rises steeply. The angle is inflected inward 

 and is rounded, not angulate anteriorly and posteriorly as in S. viciacensis (see Filhol, 

 1891, PI. 5). 



The Dentition. — The anterior face of the lower incisor is not so convex as in S. hes- 

 perus just described. The posterior angle is not so acute but is broadly rounded. The 

 outer part of the cutting edge is rounded, not angulate, and the inner worn, beveled 

 surface is long and longitudinally concave. Below this the transverse is just a trifle 

 greater than the antero-posterior diameter. 



The upper cheek teeth are very complex on account of the number and the curving 

 of the enamel lakes and inflections and the sinuosity of the enamel. This might be simpli- 

 fied on further wear. The inner loops extend forward as much as outward, and some of 



