168 The Extinct Rodentia of North America, (February, 
crown descends to its base, and hence persists longer than in the 
typical Entoptychi. ine 
I am acquainted with two species of this genus. The posterior i 
part of the skull of an individual represents a third species, which 
I refer provisionally to this genus. See Fig. 16. i 
ENTOPTYCHUS Cope. | 
Molars 4-4, rootless, and identical in structure. The crowns att 
prismatic, and in the young stage present a deep inflection of 
enamel from one side, the external in the superior teeth, the intet 
nal'in the inferior.  Aftera 
little attrition, the conneč 
tion with the external en- 
amel layer disappears, and 
there remains a mediat 
transverse fossette, entirely : 
inclosed by enamel. 
tooth then consists of 
dentinal columns in oie 
cylinder of enamel, sepr 
rated by a transverse enat 
ere =a el-bordered tube. 
- i. not sulcate: Ty 
The teeth of this 
differ from those of Feros 
nathus in being without 
tinct roots, and in hat 
the enamel loop cut o 
inclosed. In Dipoael 
bye f= 
ù 
Fic. 17.— Entoptychus crassiramis Cope ; 
a, “ gp from side and a ve; c, mandi- 
€ irom above. Natural size. From the Toh i i 
Day epoch, Oregon. Original. From aea simple PEREN i 
U: S. Geol. Survey Ters. F. V. Hayden. The skull is com 
2 l K does not display th 
ties or large foramina seen in some genera of Rodentia. 
gh deep pterygoid fossze, whose inner bounding laminæ uni 
middle of the palatine border and whose external lamine 
latter looks like a continuation of the former, as in Tho 
and occupies considerable Space between the exoccipital an 
Squamosal. The latter sends downwards a process just. 
J03 
r 
