SCIUUIDil3— EXTINCT ai'KCIES. 



937 



toctli and (heir nilntivo jmwitioii, agrei; with the conditions in Purumi/s, hut 

 the form of tlic mohirs is sufficiently dilferent to refer hlic specimen to n dif- 

 f(!rent genus, for wliicli the above luinie lias l)een j)roi)oscd. The [lower] 

 molar teeth, as in Paramys, are four in lunnher, inserted each l)y a |)air 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- 



liil»it8 three transverse ridges or lobes, of whieii the anterior is the thickest, 



(he middle one the tiiinnest, and the posterior the shortest The anterior 



molar of Mysops, like the last one, is more elongated fore and afl 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 wliich reaches as far forward as the posi- 

 tion of tbc 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 Bnttes, Wyoming. 



Animals of small size, scarcely larger than the common Mouse {Mas 

 musnulus). 



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

 but its affinities are apparently more Sciurine than Murine. 



MYSOPS FRATERNUS Lcidy. 



Myaopt fraUmm Lkidv, Kxtinct Vert. Fauna, 187;t, 112, 33C, pi. xxvii, flgs. U, 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. 



Uytogs minulut Lkiuy, Proc. Acnd. Nnt. Sci. PUila. 1871, 239; Ann. Rep. U. 8. Cool. Snrv. Terr, for 1871 

 (1878), 357 ; Extinct Vert. Fauna, 1878, 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. 



