MURID^— SIOMODONTES— REITHRODON. 



119 



alternata, and in some stages of near show a porfeot letter S, at one time auiiposcd to bu cbuructoi- 

 Istic of tbo genus Sigmodoit, but now known to be a pattern of couimou, if, indeed, it bo uut uf universal, 

 occurrence'amoug American Murtvai. 



Tlie geuUB appears to bo ooutlned to tbo southern part of South America, fruiu which tlireo siiucio^i 

 have been d'-sctibed. Two of these, tt. cunieuloidn and M. ehinchiltoida, are sharply distingiUHhed by the 

 characters already pointed out, and others ; but the diflTerences between It. cunicutoideii aud Jl. lypivai ure 

 not so clear. It Heems to us probable that the latter will prove to be, If not identical with, at most only 

 a geographical race of «Miiicii(o(({p<— 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 wo can- 

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

 genus itself, from Waterhouse's original notices. 



KEITHBODON CUNICUL0IDE8, Waterbonse. 



UMhrodon cuHiculaidei, Waterhodse, Proo. Zool. Boo. 1837, SO; Zool. Voy. Beagle, pt. ii, 09, pi. xxvi 

 (animal), pi. zzziii, figs. 2b, So, id, 2e (teeth), pi. xxxiv, figs. 2a, 2b, 2a (skull). 



DuGNOSis. — Yellowish-gray mixed with bluck ; throat and belly pale yellow; rump and fuet 

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

 long as the bead and body, bluolor, dusky above, white belo'.r. Length, 6i ; tail, 'H ; hind feet, H ; ear, }. 



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



The fiir is described as long and soft ; the general color of the upper parts is " gray isb-Urown with 

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

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

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

 the annuli, dusky abcve, white below ; incisors yellow. The dimensions of a skull are given as follows : — 

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

 a glance at plate 86 is sufficient to show the curious general appearance of the species which suggested 

 its specific name. 



■EITHBODON TYPICUS, Waterhonse. 



BeUkrtdim tfpUiu, Waterbovse, Proc. Zool. Boo. 1S37, 30 ; Zool. Voy. Beagle, pt. ii, 1839, 71, pi. xxxiii, 

 fig. 4a (teeth). 



As described, this supposed species differs from the last in being smaller, with shorter feet and 

 longer can, and of darker color. The dimensions assigned are, length, 6 inches ; hind foot, 1 inch 8i 

 lines ; ear, 6| lines. From La Plata (Maldonodo, Darwin). 



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

 from e»niimloide$. It does not appear why it was named " typicus", since the genus appears to have been 

 drawn up from the better-known oaiiuia/oidM, wbioh must stand as the type uf Jieilhrodon, B. chinchil- 

 hida was not described nnlil two years afterward. 



KEITHBODON (EUNEOMYS) CHINCUILLOIDES, Waterhonse. 



Heithrodon ckincWloida, Watbbhodsk, Zool. Voy. Beagle, 1839, pt. ii, 78, pi. xxvii (animal); pi. xxxiv, 



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

 Iteitkrodon (Buneomyt) ckinckilUridet, CouES, Proc. Aoad. Nat. Sci. Pbila. 1844, 185. 



Diagnosis. — Cinereons, 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. liCUgth, 6 inches; 

 tuil, 2i ; tarsus, 1 ; ear, hardly i. I^kull, 1^ long, 8^ lines wide. 



Habitat.— Straits of Magellan. 



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

 cnnioiloidet or igpUMii and the plate above cited shows an animal of different external appearance. It 

 is smaller, with apparently disproportionately smaller members, the color different, aud the for particu- 

 larly long and soft — a ciitinmstance snggeating its specifio name, althoogb it has, like ennicnhidn, the 

 curious rabbit-like aspect characteristic of the genus. 



