.Jm 



I 



;io 



MONOGUAl'IlS OF NORTH AMERICAN RODBNTIA. 



187G— CoL'KS (!•;.)• ConriTniiiK '• I'ockct" (iopliprH. < Aiiicricnn Sportsman of Juno 5, 1875, 

 [NCTE.~A popular iiccnutit (f (fcoiuymu'. I 



IH/f)— CoUKs (K.). TIk^ cranial mill (liMitttl cliarnpterB of Gtwinjiilm. < Ilnll. II. 8. (ieol. & Oeogr. Snrv. 

 Terr. 2(1 Mcr. nii. U, \>\i. ril-DU, May U, IWrj. [Koiirintcil, with hohio modilicutioii, ua Addeuiluni 

 A of llio memoir bt'low cited.] 



1«75— CoiJi'.s (E.). Sjuopsis of tbo Gconijidu). < Troo. I'hilo. Acad. 1875^ pp. 130-13a. [A brief 

 abHtraci of tbo u>onioir next below cited.] 



1^75— Ci>ui:k (E.). Exploration of the Colorado River of tlie Wost and its tributaries. Explored iu 

 lH(i<.), 1H70, 1871, and 1872, under tlie direction of tbo Secretary of the Smitbsonian Inxtitn- 

 ti<m. Wuxbinjjton : Government Priuting Ofilce. 1875. Part III. — Zoiilogy. By Elliott 

 Couen. Chapter XII. — AbHtroct of resultH of a stiuly of tbo genera Geoniys and TbomoniyH, 

 pp. 215-385, tig. 80. ( Reissued an separate pamphlet with tbo title "Abstract of results of a 

 study of the Kciiera Geoniys and Tboniomys, with addenda on the osteology of Geomyida) 

 and on the habits of Geoniys tiiza". The reissue only diffura from the original in the title.) 



1875— GOODE (G.B.). Notes on tho "Salamander" of Florida (Geomys tuza). < Powell's Rep. Colorado 

 R. 1875, pp. 281-285. 

 t N'OTR.— On tho liablu of tho spociua ; beiug Addendnm B of the article but cited.] 



For cliaractcis, especially in comparibon and contrast with those of Snc- 

 comyidcp., sec antea, pp. 402, 493. - - 



The cranial and dental* characters are very fully presented in my paper 

 in the Bulletin of the Survey, above cited. 



The external characters are detailed at length in the descriptions of the 

 leading species of tiic two fenera, Geomys hursarius and Thomomys talpoidm, 

 in the zoological portion of Powell's Report, above cited. 



The two genera are readily distinguished by the profoundly suicatc inci- 

 sors, enormously developed fore claws, and rudimentary ears of Geomys, con- 

 trasted with the smooth incisors, moderately fossorial claws, and distinct 

 though very small cars of Thomomys. There are also many cranial charac- 

 ters, as given beyond. The two genera offer the further curious difference, 

 that in Geomys a number of species appear to have been firmly established, 

 while the differentiation of Thomomys has not progressed so far. There is 

 probably a difference in the number of maminw in the two genera ; Thomomys 

 usually liaving six pairs, while in no Geomys have I recognized more than 

 three pairs. The pouchcsf are substantially the same in the two genera. 



* Tho dental forninia may he rendered more precisely, as follows : — 



I.?-|;C.''-'!:P.!-liM.»-=' 



0-0. p 1-1. 



5-6^10^^» 

 5—5 10 * ■ 



1—1' 0—0' 1— I'. ;i— 3 

 t "The ponchos . . . —at first supposed to he pendulous hags hanging from tlio mouth, then with 

 some correction found to ho not penilnlous, yet believed to open into the mouth from witliin — are wholly 

 cxteriial, ami have no more connection with the buccal cavity than thj belly -p<iuch of a Ksngr.roo or 

 Opos.suni has to do with the genital organs. These sacs are simply a purse-shaped duplicature of tbo 

 loose skin of the side of the head and neck. The free margin of the pouch arises from the side of tho 

 upper jaw, about half-way from noso to rye, just underneath the wh.riker-pateh, and curves loosely 

 around the siile of the bead to the angle of the jaw. The general ontliuo of tho orifice is semicircular 

 (or rather semipyrifuriii, si.ico the broadest p- •» ■' 'vu a little); the inner border being the proper 



iutegumeut of the sido of tho head. Tbo linin,^ aoo in ordinary integnment, of rather moru deU- 



d:i.^ 



