610 MONCGRAPHS OF NORTIM AMERICAN RODENTIA. 
1875— Cours (.). Concerning “ Pocket” Gophers. < American Sportsman of June 5, 1875. 
[Netr.—A popular account cf Geomyidw. } 
1875—CouErs (E.). The cranial and dental characters of Geomyidw. < Bull. U. S. Geol. & Geogr. Surv. 
Terr. 2d ser. no. 2, pp. 81-90, May 11,1875. [Reprinted, with some modification, as Addendum 
A of the memoir cicliier cited.] 
1875—Covurs (E.). Synopsis of the Geomyidw. < Proc. Phila. Acad. 1875, pp. 130-138. [A brief 
abstract of the memoir next below cited. ] 
1s75—Cours (E.). Exploration of the Colorado River of the West and its tributaries. Explored in 
1869, 1870, 1871, and 1872, under the direction of the Secretary of the Smithsonian Institu- 
tion. Washington: Gaveeenent Printing Office. 1875. Part II.—Zodlogy. By Elliott 
Coues. Chapter XII.—Abstract of results of a study of the genera Geomys and Thomomys. 
pp. 215-285, fig. 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 Geomyida 
and on the habits of Geomys tuza”. The reissue only differs from the original in the title.) 
1875—Goopr (G.B.). Notes on the ‘“ Salamander” of Florida (Geomystuza). < Powell’s Rep. Colorado 
R. 1875, pp. 281-285. 
[NorEe.—On tho habits of the species; being Addendum B of the article last cited.) 
For characters, especially in comparison and contrast with those of Sac- 
comyida, 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 talpordes, 
in the zodlogical portion of Powell’s Report, above 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 ears 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 mamme in the two genera; Thomomys 
usually having six pairs, while in no Geomys have I recognized more than 
tree pairs. The pouchest are substantially the same in the two genera. 
* The fara Gann may be rendered more precisely, as follows :— 
= “5 7 = 1—1 3—3_ _5—5_ 10 
1 fe Y —>; Br 
Si Mie es ibe 
t“‘The pouches . . . —at first ear to be pendulous 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 haye 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 duplicature of the 
loose skin 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 the 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 the side of the head. The lining of the sac is ordinary integument, of rather more deli- 
