(310 MONOGRAPHS OF NORTE AMERICAN RODENTIA. 



1675— Coi i - r..). Concerning " Pocket " Gophers. < American Sportsman of June 5, 1875. 

 i \ popular nc ounl i i * taomj khe. ) 



1875— i "i E8 (E.). The cranial and deutal characters of Geomyidte. < Bull. IT. S. Geol. &. Geogr. Snrv. 

 I ■ rr. 26 sor. ii". '.'. pp. 81-90, May 1 L, L875. [ Reprinted, with some modification, as Addendum 

 A of the memoir below cited.] 



1875 — Couics (E.). Synopsis of the Qeomyidse. < Proc. Phila. Acad. 1875, pp. 130-138. [A brief 

 abstract, of the memoir next below cited.] 



1-7.V- COUE8 (E.). Exploration of the Colorado River of the West and its tributaries. Explored iu 

 lS(>i>, 1*70, 1871, and 1*72, under t ll^^ direction of the Secretary of the Smithsonian Institu- 

 tion. Washington : Government Printing Office. 1875. Part, III. — Zoology. By Elliott 

 Cones. Chapter XII. — Abstraet of results of a study of the genera Geomys and Thomomys. 

 pp. 215-285, tig. 80. (Reissued as separate pamphlet with the title "Abstract of results of a 

 study of the genera Geomys and Thomomys, with addenda on the osteology of GeomyidsB 

 and on the habits of ( '• oys tuza". The reissue only differs from the original in the title.) 



187")— Goodk (G. I!.). Notes on the '' Salamander" of Florida (Geomys tuza). < Powell's Rep. Colorado 

 R. 1875, pp. 281-285. 

 [Note. — On the habits of the species ; being Addendum B of the article last citod.] 



For characters, especially in comparison and contrast with those of Sac- 

 comyidcp, see anted, pp. 492, 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 the two genera, Geomys bursarius and Thomomys talpoides, 

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



The two genera are readily distinguished by the profoundly sulcate 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, 

 1 hat 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 mamma? in the two genera ; Thomomys 

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

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



* The dental formula may he rendered more precisely, as follows: — 



t 1-1. r 0-0. p 1-1. M 3-3_5-5_10_™ 



L i— i ' C ' 5=0 > R f=I ' M - 3=3-5=5- is- a0 - 



t"The pouches . . . — at first supposed to be pemlulons bags hanging from the mouth, then with 

 some correction found to be not pendulous, yet believed to open into the mouth from within — are wholly 

 external, and have no more connection with the buccal cavity than the belly-pouch of a Kangaroo or 

 Opossum has to do with the genital organs. These sacs are simply a purse-shaped duplicative of the 

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

 upper jaw, about half way from nose to eye, just underneath the whisker-patch, and curves loosely 

 around the side of the head to the angle of tin- jaw. The general outline of the orifice is semicircular 

 (or rather semipyriform, since the broadest part sags down a little); the inner border being the proper 

 integument of tho side of the head. The lining of the sac is ordinary integument, of rather more deli- 



