MURIDiE— SIGMODONTES— EEITORODON. 1 19 



alternate, ami in some stages of wear show a perfect letter S, at one time supposed to l>o character- 

 istic of tho genus Sigmodon, but now known to be a pattern of common, if, indeed, it bo not of universal, 

 occurrence among American Marina:. 



The genus appears to bo confined to the southern part of South America, from which three species 

 have been described. Two of these, It. cuniculoides and R. chiuchilloides, are sharply distinguished by the 

 characters already pointed out, and others; but the differences between R. cuuicu hides and R. lypicus are 

 not so clear. It seems to us probable that the latter will prove to bo, if not identical with, at most only 

 a geographical race of cuniculoides — the ascribed characters appear, according to our experience with this 

 family, to be within an ordinary range of variation in the same species. But without specimens we can- 

 not, of course, presume to say that such is the case; and we redescribe the three species, as wo have tho 

 genus itself, from Waterhouse's original notices. 



EEITHKODON CUNICULOIDES, Waterhouse. 



Reithrodon cuniculoidee, Waterhouse, Proc. Zool. Soc. 1837, 30; Zool. Voy. Beagle, pt. ii, 09, pi. xxvi 

 (animal), pi. xxxiii, figs. 26, 2c, 2d, 2c (teeth), pi. xxxiv, figs. 2a, 26, 2c (skull). 



Diagnosis. — Yellowish-gray mixed with black; throat and belly pale yellow; rump and feet 

 white; ears of medium size ; yellowish, with a yellowish-white patch behind them; tail about half as 

 long as the head and body, bicolor, dusky above, white below. Length, 04 ; tail, 3£ ; hind feet, 1J ; ear, J. 



Habitat. — Patagonia (Port Desire, Saint Julian, Santa Cruz; Darwin). 



The fur is described as long and soft ; the general color of the upper parts is "grayish-brown with 

 a considerable admixture of yellow "; the sides are yellowish-gray, paler below, fading into yellowish- 

 white underneath, and there is a patch of the same behind the ears, which are also yellowish; mous- 

 taches very long and numerous, black and gray ; soles partly hairy ; hairs of the tail sufficient to hide 

 the an mil i, dusky above, white below; iucisors yellow. The dimensions of a skull are given as follows: — 

 Length, 1^ ; width, ft. The teeth are very satisfactorily figured, enlarged in the plate above cited, while 

 a glance at plate 20 is sufficient to show the curious general appearance of the species which suggested 

 its specific namo. 



REITHRODON TYPICUS, Waterhouse. 



Reithrodon typhus, Waterhouse, Proc. Zool. Soc. 1837, 30 ; Zool. Voy. Beagle, pt. ii, 1839, 71, pi. xxxiii, 

 fig. Aa (teeth). 



As described, this supposed species differs from tho last in being smaller, with shorter feet, aud 

 longer ears, and of darker color. The dimensions assigned are, length, inches; hind foot, 1 inch 2^ 

 lines; ear, 8£ lines. From La Plata (Maldonado, Darwin). 



As already intimated, we admit the species on probation, suspecting it will not prove distinct 

 from cuniculoides. It does not appear why it was named " typieus", since the genus appears to have been 

 drawn up from the better-known cuniculoides, which must stand as the type of Reithrodon. It. chinchil- 

 loidts was not described until two years afterward. 



REITHRODON (EUNEOMYS) CHINCHILLOIDES, Waterhouse. 



Reithrodon chiuchilloides, Waterhouse, Zool. Voy. Beagle, 1839, pt. ii, 72, pi. xxvii (animal); pi. xxxiv, 



figs. 20a, 206, 20c, 2Qd, 20c, 20/ (skull and teeth). 

 Reithrodon (Euneomys) chincMlloides, Coues, Proc. Acad. Nat. Sci. Phila. 1844, 185. 



Diagnosis. — Cinereous, washed with yellowish-dusky, under parts yellowish-white; tail dusky 

 above, white below, half as long as the head and body ; ears and tarsi rather short. Length, 5 inches; 

 tail, 2J ; tarsus, 1 ; ear, hardly -J. Skull, \' s long, 8^ lines wide. 



Habitat.— Straits of Magellan. 



We have already detailed the notable structural characters by which this species differs from 

 cuniculoides or typieus; and the plate above cited shows an animal of different external appearance. It 

 is smaller, with apparently disproportionately smaller members, the color different, and tho fur particu- 

 larly long and soft — a circumstance suggesting its specific name, although it has, like cuniculoides, the 

 curious rabbit-like aspect characteristic of the genus. 



