CJiAP. XVII.] 



MAMMALIA. 



233 



Family 50.— SACCOMYIDiE. (G Genera, 38 Species ) 



The Saccomyidip, or pouched rats, are ahnost wholly confined 

 to our second ISTearctic snl3-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 

 ■\ve.st, 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, — DijJodonnjs (5 sp.), North Mexico, California, 

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

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

 California, east slope of the Eocky jMountains to British 

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

 Columbia Eivers to Hudson's Bay ; Gcomy^ (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 ; Hderumys (6 sp.), Mexico, Honduras, and Trinidad. 

 Geomys and TJwmomys 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 Geomys have been found. 



