SCIUltlD^— 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 arc 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 on a 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 

 mu sculus). 



This genus was doubtfully referred by Dr. Leidy, in 1873, to the Muridce, 

 but its affinities are apparently more Sciurinc than Murine. 



MYSOPS FRATERNUS Leidy. 



Mysops fraternus Leidy, Extinct Vert. Fauna, 1873, 112, 336, pi. xxvii, figs. 14, 15. 



Size of the common Mouse (Mus ?nusculus). 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. Pbila. 1871, 232; Ann. Eep. U. S. Geol. Surv. Terr, for 1871 

 (1872), 357; Extinct Vert. Fauna, 1873, 111, 336, pi. vi, figs. 31, 32. 



Size of the last. Described from a ramus of the lower jaw, containing 

 two molars. Grizzly Buttes, Wyoming. 



