PALHIONTOLOGICAL APPENDIX—EXTINCT RODENTIA. 945 
The species was described from the greater portion of a skull and several fragments 
of lower jaws, discovered by Dr. Hayden in the Mauvaises Terres of Bear Creek (a 
tributary of the Sheyenne River) and White River, in beds of Miocene age. 
The genus has been referred by Dr. Leidy and Professor Cope to the Sciuride, but 
evidently pertains to a distinct family, as shown by the large infraorbital foramina, the 
absence of postorbital processes, the great interparietal constriction of the skull, ete. 
Incerte sedis.* 
GENUS GYMNOPTYCHUS Cope. 
Gymnoptychus Corr, Pal. Bull. no. 16, 1873, 5; “Ann. Rep. U.S. Geol. Surv. Terr. tor 1873 (1874), 476. 
“The essential features are, dentition; I. 4; C. 8; M.4; the molars with two cres- 
cents on the inner side above, each of which gives rise to a cross-ridge to the outer 
margin. In the mandibular series the crests and crescents have a reversed relation. 
No cementum.” Gymnoptychus chrysodon, the first species referred to this genus by its 
describer, is said to have no postorbital processes. The skull is said to be broad and 
stout, but not depressed, with the muzzle broad and short, and *‘the front” (frontal 
region?) moderately contracted. While its dentition is somewhat Sciurine, the absence 
of postorbital processes renders its reference to the Sciwride quite doubtful, although it 
has been thus referred by Professor Cope.t Several species of this genus have been 
described by Professor Cope from the “ Tertiary of the Plains”; but their exact locality 
of occurrence is not indicated. ¢ 
GYMNOPTYCHUS CRYSODON Cope. 
Gymnoptychus crysodon Cory, Pall. Bull. no. 16, 1873, 5. 
“ First upper molar a single cone. Incisors quite compressed. First inferior molar 
a broad oblong, the cusps opposite, the anterior close together. The two posterior 
cross crests do not form a V, the anterior being interrupted at the cusp. There is ¢ 
delicate tubercle between the outer cusps of the three last molars. The incisor is com- 
pressed, the anterior and outer faces being separated by an angle.” 
GYMNOPTYCHUS NASUTUS Cope. 
Gynnoptychus nasutus Core, Pal. Bull. no. 16, 1873, 6. 
Muzzle much compressed; nasal bones flat, extending beyond the upper incisors. 
Much smaller than the last, with the first molar narrower. Inferior molars with two 
cross-crests and two cingulz from the exterior cones, each posterior crest terminating 
in an interior cone. 
GYMNOPTYCHUS TRILOPHUS Cope. 
Gymnoptychus trilophus Cor¥, Pal. Bull. no. 16, 1873,6; Ann. Rep. U.S. Geol. Sury. Terr. for 1873 (1874), 476 
Intermediate in size between the two preceding. Molars with two cross-erests, not 
connected by cingula. 
GYMNOPTYCHUS MINUTUS Cope. 
Gymnoptychus minutus Cork, Pal. Bull. no. 16, 1873, 6; Ann. Rep. U.S. Geol. Sury. Terr. for 1873 (1874), 476. 
Very small, scarcely larger than a House Mouse (Jlus musculus), and differs from 
the others somewhat in dentition. 
* The genera next following (Gymnoptychus and Pseudotomus) are evidently Sciuromorphs, aud may 
both be referable to the family Ischyromyide. 
t Ann. Rep. U. 8S. Geol. and Geog. Sury. Terr. for 1873 (1874), 474. 
} Professor Cope, in his second notice of this genus (I. ¢.), says, ‘Two species are known, a larger 
and a smaller”; and then follow notices of G. trilophus and G. minutus, with no reference whatever to 
G.erysodon and G. nasutus, described by him at the same time G. trilophus and G. minutus were described! 
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