SCIURIDM—EXTINCT SPECIES. 937 
teeth and their relative position, agree with the conditions in Paramys, but 
the form of the molars is sufficiently different to refer the specimen to a dif- 
ferent genus, for which the above name has been proposed. The [lower] 
molar teeth, as in Paramys, are four in number, inserted each by a pair of 
fangs. ‘The crowns are quadrate and invested with enamel. The triturating 
surface, instead of being constructed like that of the Squirrels, is more like 
that of the Rats. .... The crown of the third molar exhibits two trans- 
verse lobes, or ridges, joined by an intermediate narrow ridge, and the inner 
surface of the lobes include a trilateral tubercle. .... The last molar ex- 
hibits three transverse ridges or lobes, of which the anterior is the thickest, 
the middle one the thinnest, and the posterior the shortest. .... The anterior 
molar of Mysops, like the last one, is more elongated fore and aft than the two 
succeeding molars, but is proportionally of less size than in the Rats, and has 
not three fangs, as in these animals. .... The jaw is proportionately deep 
and short, compared with that of the Rat. The masseteric fossa is deep, and 
defined by a rectangle, the apex of which reaches as far forward as the posi- 
tion of the third molar tooth. The border of the jaw at the hiatus in advance 
of the molars extends nearly ona level from their alveoli to that of the inci- 
sor.’ The skull remains unknown. Described from remains found by Dr. 
Carter at Grizzly Buttes, Wyoming. 
Animals of small size, scarcely larger than the common Mouse (Mus 
musculus). 
This genus was doubtfully referred by Dr. Leidy, in 1873, to the Murida, 
but its affinities are apparently more Sciurine than Murine. 
MYSOPS FRATERNUS Leidy. 
Mysops fraternus Leipy, Extinct Vert. Pauna, 1873, 112, 336, pl. xxvii, figs. 14, 15. 
Size of the common Mouse (Mus musculus). Described from a portion 
of a right ramus of a lower jaw containing the last three molars. Length 
of the molar series about 0.26 of an inch; depth of the jaw at the third molar 
0.21. Grizzly Buttes, Wyoming. 
MYSOPS MINUTUS Leidy. 
Mysops minutus LEIDy, Proc. Acad. Nat. Sci. Phila. 1871, 232; Ann. Rep. U. 8. Geol. Surv. Terr. for 1871 
(1872), 357; Extinct Vert. Fauna, 1873, 111, 336, pl. vi, figs. 31, 32. 
Size of the last. Described from a ramus of the lower jaw, containing 
two molars. Grizzly Buttes, Wyoming. 
