PALiEONTOLOGICAL APPENDIX— EXTINCT RODENTIA. 



945 



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

 of lower jaws, discovered by Dr. Hayden in tbe Mauvaises Terres of Bear Creek (a 

 tributary of the Sheyenue River) and White Biver, in beds ot Miocene age. 



The genus has been referred by Dr. Leidy and Professor Cope to the Sciuridw, 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 sedu.* 

 GENtJS GYMNOPTY0HU8 Cope. 



Oymnoplychtu Cope, Pol. Ball. no. 16, 1873, 5; Adu. Eep. U. 8. Geol. Surv. Terr, for 1873 (1874), 476. 



"The essential features are, dentition ; 1. 1 ; C. J ; M. f ; the molars with two cres- 

 cents on the inner s|de above, each of which gives rise to a cross-ridge to the outer 

 margin. In the mandibular series tbe crests and crescents have a reversed relation. 

 No cementum." Qymnoptychus chrysodon, the first s|)ecies refeiTcd 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 T) moderately contracted. While its dentition is somewhat Sciurine, tbe absence 

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

 has been thus referre.1 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. X 



0YMN0PTYCHU8 CRY80D0N Cope. 

 Qnmnopti/tMHs crynxfen Cope, Fall. Ball. do. 16, 1873, 5. 



" First upper molar a single cone. Incisors quite compressed. First inferior molar 

 a broad oblong, the cusps opposite, tbe anterior close together. The two posterior 

 cross crests do not form a V, the anterior being interrupted at the cusp. There is a 

 delicatr> tubercle between tbe onter cusps of the three last molars. The incisor is com- 

 pressed, the anterior and outer faces being separated by an angle." 



GYMN0PTYCHU8 NASUTUS Cope. 



Gjimnoptjichiu naauliu Cope, Pal. Bull. no. 16, 1873, 6. 



Muzzle luuch 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 cinguloe from tbe exterior cones, each posterior crest terminating 

 in au interior cone. 



GYMNOPTYCHUS TKILOPHUS Cop«. 



OyvmoplyQhiu Mlophua Cope, Pal. BaU. no. 16, 1873, 6 ; Add. Bep. U. 8. Geol. Sarv. Terr, for 1873 (1874), 476 



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

 connected by oingula. 



OYMNOPa'YCHU8 MlNUTUg Cope. 



Gymiioplyehiu miHutui Cope, Pol. Bull. no. 16, 1873, 6 ; Ann. Kep. U. 8. Geol. Surv. Terr, for 1873 (1874), 476. 



Very small, scarcely larger tliau a House Mouse (Mm viusoulwi), and differs from 

 the others somewhat in dentition. 



* The genera next following {Oj/mmplychut and Pneudolamiu) are evidently Scinromorphii, and uiuy 

 both be referable to the family Itdiyromyida. 



t Ann. Rep. U. 8. Geol. and Geog. Surv. Terr, for 1873 (1874), 474. 



I Ptofeaeor Cu|>e, in bie second notice of this genns (I. c.). Buys, " Ttvo gpecien are known, a larger 

 and a ■mailer"; and then follow notices of (i. Irilophiu and G. nifnu(Mi, witb no reference whatever to 

 Q.crytodnn and G. najittm, described by biui at the same time 0, tritophn» auii O. minnluii were dcsuribedl 



