MURIDA—SIGMODONTES—REITHRODON. 119 
alternate, and in some stages of wear show a perfect letter S, at one*time supposed to be character- 
istic of the genus Sigmodon, but now known to be a pattern of common, if, indeed, it be not of universal, 
occurrence among American Murine. 
The genus appears to be confined to the southern part of South America, from which three species 
have been described. Two of these, R. cuxiculoides and 2. chinchilloides, are sharply distinguished by the 
characters already pointed out, and others; but the differences between 2. cuniculoides aud 2. lypicus are 
not so clear. It seems to-us probable that the latter will prove to be, 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 we have the 
genus itself, from Waterhouse’s original notices. 
REITHRODON CUNICULOIDES, Waterhouse. 
Teithrodon cuniculoides, WATERHOUSE, Proce, Zool. Soc. 1837, 30; Zool. Voy. Beagle, pt. ii, 69, pl. xxvi 
(animal), pl. xxxiii, figs. 2b, 2c, 2d, 2e (teeth), pl. xxxiv, figs. 2a, 2b, 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, 64; tail, 34; hind feet, 14; ear, #. 
Hawirat.—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 annuli, dusky above, white below; incisors yellow. The dimensions of a skull are given as follows :— 
Length, 14; width, &. The teeth are very satisfactorily figured, enlarged in the plate above cited, while 
a glance at plate 26 is sufficient to show the curious general appearance of the species which suggested 
its specific name.* 
REITHRODON TYPICUS, Waterhouse. 
Reithrodon typicus, WATERHOUSE, Proc. Zool. Soc. 1837, 30; Zool. Voy. Beagle, pt. ii, 1839, 71, pl. xxxiii, 
fig. da (teeth). 
As described, this supposed species differs from the last in being smaller, with shorter feet and 
longer ears, and of darker color. The dimensions assigned are, length, 6 inches; hind foot, 1 inch 24 
lines; ear, 84 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 ‘“ typicus”, since the genus appears to have been 
drawn up from the better-known cuniculoides, which must stand as the type of Reithrodon. Rk. chinchil- 
loides was not described until two years afterward. 
REITHRODON (EUNEOMYS) CHINCHILLOIDES, Waterhouse. 
Reithrodon chinchilloides, WATERHOUSE, Zool. Voy. Beagle, 1839, pt. ii, 72, pl. xxvii (animal); pl. xxxivy, 
figs. 20a, 20b, 20c, 20d, 20e, 20f (skull and teeth). 
Reithrodon (Euneomys) chinchilloides, Cours, Proc. Acad. Nat. Scit 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 inehes; 
tail, 24; tarsus, 1; ear, hardly 4. Skull, 14 long, 84 lines wide. 
HapitatT.—Straits of Magellan. 
We have already detailed the notable structural characters by which this species differs from 
cuniculoides or typicus; and the plate above cited shows an animal of different external appearance. It 
is smaller, with apparently disproportionately smaller members, the color different, and the 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. 
