PAL.EONTOLOGICAL APPENDIX— EXTINCT RODENTIA. 945 



The species was described from the greater portion of a skull and several fragments 

 of lower jaws, discovered by Dr. Haydeu in the Mauvaises Terres of Bear Creek (a 

 tributary of the Sheyeuue River) and White Eiver, in beds ot Miocene age. 



The genus has been referred by Dr. Leidy and Professor Cope to the Sduridce, 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, etc. 



Incertw s.edis* 

 Genus GTMNOPTYCDUS Cope. 



Gijmmptychws Cope, Pal. Bull. no. 16, 1873, 5 ; Ann. Rep. U. S. Geol. Surv. Terr, lor 1873 (1874), 476. 



"The essential features are, dentition ; I. A; C. g; M. f ; the molars with two cres- 

 ceuts 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." Gymnoptychiis 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 aud short, and "the front'' (frontal 

 region !) moderately contracted. While its dentition is somewhat Seiuriue, the absence 

 of postorbital processes renders its reference to the Sciuridce quite doubtful, although it 

 has beeu 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. 



Gymnoptychiis crysodon Cope, Pall. Bull. uo. 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 a 

 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. 



Gymnoptychtu nasutus Cope, 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 aud two cingulse from the exterior cones, each posterior crest terminating 

 in an interior cone. 



GYMNOPTYCHUS TRIUOPHUS Cope. 



Gymnoptychiis trilophus Cope, Pal. Bull. no. 16, 1873, 6; Ann. Eep. U. S. Geol. Surv. Terr, for 1873 (1874), 476 

 Intermediate in size between the two preceding. Molars with two cross-crests, not 

 connected by ciugula. 



GYMNOPTYCHUS M1NUTUS Cope. 



Gymnoptychiis minutus Cope, Pal. Bull. no. 16, 1873, 6 ; Ann. Eep. U. S. Geol. Suvv. Terr, for 1873 (1874), 476. 

 Very small, scarcely larger than a House Mouse [Mm musculus), and differs from 

 the others somewhat in dentition. 



* The genera next following (Gymnoptychiis and Pseudotomus) are evidently Scinromorphs, and may 

 both be referable to the family Ischyromyidce. 



t Ann. Rep. U. S. Geol. and Geo;,'. Surv. Terr, for 1873 (1874), 474. 



i Piofessor Cope, in his second notice of this genus (1. a), says, "Two species are known, a larger 

 and a smaller"; and then follow notices of G. Irilophus and G. minutus, with no reference whatever to 

 G. crysodon and G. najutus, described by him at the same time G. triloph us aud G. minutus were described! 



60 M 



