PETERSON : DESCRIPTION OF NEW RODENTS 141 
P+ is the only superior check-tooth that retains the internal enamel-fold after 
the maturity of the animal. All the other teeth seem to have lost this character 
early, the surrounding enamel-bands showing no folding. 
In the cotype (PI. XVIL., Fig. 3) there is a slight dissimilarity in the enamel pat- 
tern of the crowns of the premolars on opposite sides. The anterior fossette of the 
right premolar is oblong, and is the continuation of the internal enamel-fold, while 
on the tooth on the left side this fossette is smaller and rounded, and the anterior 
island is apparently independent of the internal enamel-fold. On the external 
enamel-band there remains a slight indication of the folding, which is shown only 
in the cotype in our series of skulls. There is also a small rounded fossette near the 
postero-external angle on both premolars, a character not found in the type. 
Molar + is broader than long in the cotype, while in the type its diameter is 
nearly equal in both directions giving it a subcylindrical form. There are three 
fossettes on the grinding face, one antero-external and transverse, the other antero- 
a 
Le 
A)) d 
m3 m2 mi p# 
Fic. 1. Crown view of superior grinders of Steneofiber Fia. 2. Crown view of inferior grinders of Stencofiber 
fossor representing different stages of wear. a, type, No. fossor. a, type, No. 1217; b, cotype, No. 1208; ¢, an 
1217 ; b, cotype, No. 1208; ¢, an old individual, No. 1207. individual showing p; im a nearly unworn stage ; d, in 
Figures natural size. ternal view of same specimen as c, No. 453. Figures nat- 
ural size. 
internal and oblique, while the third isa large fossette occupying an oblique posi- 
tion on the postero-external part of the tooth. 
Molars 2 and 3. So far as the numbers and positions of the fossettes on 
molars 2 and * are concerned they are like the premolars. The last molar in 
the type is smaller than in any of the other skulls in the Carnegie Museum series. 
THE Inrertor Dentirron. 
The inferior incisor is as large and as strong as the superior, and is similar to 
that of the recent beaver, excepting that in our fossil form, the anterior face of the 
tooth is flat. This is characteristic throughout the entire series. The left premolar 
is injured in the type, but the corresponding tooth on the right side is complete 
The anterior fossette is still connected with the enamel band, while that on the oppo- 
site tooth is free. This tooth (p,;) has the three transverse fossettes and the external 
