CHAP. XVII.] 



MAMMALIA. 



233 



FAMILY 59. SACCOMYID.E. (6 Genera, 3^&pecies.) 



GENERAL DISTRIBUTION. 



The Saccomyidse, or pouched rats, are almost wholly confined 

 to our second Nearctic sub-region, comprising the Eocky Moun- 

 tains and the elevated plains of Central North America. A few 

 species range from this district as far as Hudson's Bay on the 

 north, to South Carolina on the east, and to California on the 

 west, while one genus, doubtfully placed here, goes south as far 

 as Honduras and Trinidad. The group must therefore be consi- 

 dered to be pre-eminently characteristic of the Nearctic region. 



The genera are, Dipodomys (5 sp.), North Mexico, California, 

 the east slope of the Eocky Mountains to the Columbia Eiver, and 

 one species in South Carolina ; Perognatkus (6 sp.), North Mexico, 

 California, east slope of the Eocky Mountains to British 

 Columbia; Thomomys (2 sp.), Upper Missouri^ and Upper 

 Columbia Eivers to Hudson's Bay ; Geomys (5 sp.), North Mexico, 

 and east slope of Eocky Mountains to Nebraska (Plate XIX., 

 vol. ii. p. 129) ; Saccomys (1 sp.), North America, locality un- 

 known ; Heteromys (6 sp.), Mexico, Honduras, and Trinidad. 

 Geomys and Thomomys constitute a separate family Geomyidse, 

 of Professor Carus ; but I follow Professor Lilljeborg, who has 

 made a special study of the Order, in keeping them with this 

 family. 



In the Post-Pliocene deposits of Illinois and Nebraska, remains 

 of an existing species of Gtomys have been found. 



