PETERSON : DESCRIPTION OF NEW RODENTS 173 
they do not furnish a reliable basis for specific determination. It seems, however, 
from figures by Cope and Matthew, that the superior grinders retain the enamel 
invaginations to a comparatively old age. The teeth are larger in comparison with 
the skull, than they are in 8S. fossor. The posterior narial opening is placed more 
anteriorly. The tympanic bulla is larger and more oblique, and “the meatal bor- 
ders are produced into a short tube which is not-so long as that of [Castor] fiber,” 
and the zygomatic arch is less expanded. Cope says that the malar bone is “ much 
expanded in a vertical direction, but has no postorbital angle, resembling in this 
respect the S. viciacensis rather than C. fiber.’ The side view (‘Tert. Vert., PI. 
LXIIL., fig. 18) of Cope’s illustrations shows a slight postorbital process. 
STENEOFIBER GRADATUS Cope. 
(Paleontological Bulletin, No. 30, 1878, p. 1; Pr. Am. Philos. Soc., 1878, p. 63 ; ” 
Tertiary Vertebrata, pp. 844, 345.) ‘ 
The type of this species, as that of S. peninsulatus, is from the John Day forma- 
tion (Diceratherium beds?) of Oregon, and is much smaller.  “ The superior incisors 
are flat anteriorly, with external angle rounded, and its dentine presents the trans- 
verse undulation seen in S. pansus. . . . The middle line of the basioccipital bone 
is keeled, with a fossa on each side. The tympanic meatus is prolonged, and the 
post-tympanic process is short.” 
In the revision by Matthew, referred to above, the*following characteristics of 
this species are given. ‘Short, wide muzzle, postorbital- constriction moderate, 
brain-base short and rounded, temporal crests not uniting to form a single sagittal 
crest for some distance back of the postorbital constriction. Bullee of moderate 
size; grinding series of teeth near together anteriorly, divergent posteriorly. The 
teeth decrease in size from p* to m® more than they do in S. neébrascensis or 
S. peninsulatus ; there is but one fossette anterior to the external enamel inflection 
on the type, while our referred specimen of S. nebrascensis shows two, neither near 
extinction, although the teeth have attained the same stage of wear.” 
STENEOFIBER PANSUS Cope. 
(Proc. Philad. Acad., 1874, p. 222; Ann. Rep. Chief of Engineers, 1875, II., p. 
993; U.S. Geogr. Surv. West of 100th Meridian, Vol. IV., 1877, pp. 297-300). 
The type of this species consists of fragments of two individuals associated. 
These were found in the Santa Fé Marls in New Mexico. The horizon is not satis- 
factorily determined. Dr. Matthews (Bull. Am. Mus., Vol. XX., 1904, p. 258), 
says: “We suspect from certain allusions in Professor Cope’s descriptions that the 
