130 PROCEEDINGS OF THE ACADEMY OP 



SYNOPSIS OF THE GEOMYIDiE. 1 



BY DR. ELLIOTT COUES, U. S. A. 



FAMILY GEOMYIDIE. 



The presence of enormous external cheek-pouches, unconnected 

 with the mouth, distinguishes this family of rodents from others 

 excepting its nearest allies, Saccomyidee ; which latter, sharing 

 the pouches, differ in the comparative length of the fore and hind 

 limbs, the great length of the tail, size of the eyes and ears, and 

 non-fossorial character of the fore feet. There are numerous and 

 more important anatomical characters, especially in the skulls. 

 The family Geomyidse, equivalent to the Sciuro-spalacoides of 

 Brandt, and to the subfamily Geomyinse of Baird, consists of two 

 genera, Geomys and Thomomys, readily distinguished as follows: 



Geomys. Superior incisors with a deep groove near the middle, 

 with or without a second fine groove along the inner margin. 

 Claws of fore feet enormously developed. External ears obsolete. 



Thomomys. Superior incisors without a central groove, but with 

 a fine groove along the inner margin. Fore claws weaker. Ex- 

 ternal ears distinct. 



Geomys has become fairly differentiated into a considerable 

 number of species, while of Thomomys all the species hitherto 

 described may be reduced to one, with three marked geographical 

 races, the intergradation between which is still complete. All the 

 described species of both genera are accounted for in the following 

 pages, excepting one, recently published by Peters (Monatsb. 

 Acad. Wissen. Berlin, 1864, p. 177), which I have not seen. 



I. Genus GEOMYS (ex Raf. ) . 



Mus, sp., Shaw et al., 1. c. infra. 



Cricetus, sp., Desm. et al., 1. c. infra. 



Geomys, Raf., Am. Month. Mag. ii. 1817, 45. 



Diplostoma, Raf., op. loc. cit. ; charact. plerumq. inept. Nee Rich. 



Saccophorus, Kuhl, Beit. 1820, 65. 



Pseudostoma, Say, Long's Exp. R. Mts. 1823, 40G. 



Ascomys, Licht. Abh. Acad. Berl. fur 1822-3, 1825, 20. 



1 This paper is an abstract of results reached in a protracted study of the 

 family, based upon the material in the National Museum, Smithsonian 

 Institution, Washington, D. C. The extended memoir will be published 

 elsewhere. 



