feet vei-}- long. 1st and 5th toes subeqnal and veiy short; fore- 

 feet not half as long as the hind. Tail nearly naked. Dental and 

 cranial characters slight. I can find but one species. 



1. Sigmodon Mspidus, Say and Ord. 



Syn. Sigmodon Mspidum, Say and Ord, J. A. N. S. P. iv. 1825, 354, pi. 



X. f. 5, 6, 7, 8; and of authors. 

 Armcola Mspidus, Godm., Am. Nat. Hist. ii. 1826, 68. 

 Arvicolu hortensis, Harlan, Fn. Amer. 1825, 138. 

 Arvicokc ferruc/iiieus, Harl., Am. Joiirn. Sc. x. 1826, 285 (rusty var.). 

 Arvicola texinna, Aud. and Bach., Q. N. A. iii. 1853, 229, pi. cxlvii. 



fig. 2 (not A. texiana, Id., ibid. 319, which is IleKperomys leucopus). 

 Sigmodon berlandieri, Bd., P. A. N. S. P. vii. 1855, 333; M. N. A. 



1857, 504 ; Mex. B. Surv. ii. 1859, 44, pi. vi. f. 2, 2a (Texas and 



Mexico),— Tomes, P. Z. S. 1861, 281 (Guatemala). 

 Hei^peromya iBeilemyi^) toltecm, De Saussurc, R. & M. Z. 1860. p. — , 



pi. ix. f. 3a (Vera Cruz). 



Hab. Sonthern United States and Mexico, especially coastwise. 

 South to Guatemala. 



Obs. Occupying a considerable stretch of country that affords 

 very different climatic conditions, this species changes insensibly 

 from reddish-brown lined with black, beneath whitish, tail rarely 

 equalling the body alone, and hind foot not over 1.30 or under 

 1.10 (typical hispidiis), to a grayer brown, with purer white under 

 parts, tail sometimes equalling body and head, hind foot some- 

 times 1.37 ('■'■ berlandie?-^') ; and this to an animal like the first in 

 colors and proportionate length of tail, but the hind foot not over 

 1.10, sometimes only 0.95 ("<o/^eci<8"). 



Genus IV. HESPEROMYS,' Waterh., emend. 



Stn. Mm, sp., Aud. — Arvicola, sp., Harl., Am. Monthly Jouru. 1832, 

 446 (nuttaUi) ; Aud. & Bach., Q. N. A. (sonoriensis Le C, texana, 

 Woodh., o,nd ort/zivom, Aud. and Bach.). — IlypiidcBus, sp., Maxim., 



' In proposing Hei^peromys, Waterhouse obviously intended only to sepa- 

 rate the New World mice collectively from those of the Old World, on the 

 difference in the dentkion. This is evident throughout his article in the 

 Voyage of the Beagle. Though treating only of South American species, 

 he is at pains to say in one place that " J/ws leucopits, Neotoma and Sigmodon 

 certainly belong to the same group." As instituted, Hesperomys is pre- 

 cisely coec|ual with the tribe or series Sigmodontes as contrasted with 

 typical Old World Mures. It includes in South America, Calomys {Eligmo- 

 dontia, F. Cuv.), ILibrothrix, Phyllotix, Scapteromys, Oxymicterus, Holo- 

 cheilufi, and Eeithrodon ; in North America, the '■^Hesperomys'''' of our 

 autliors, Onychomys, Oryzomys, '■^ Reithrodon'''' of our authors, Sigmodon 



