1882.J MR. O. THOMAS ON RODENTS FROM PERU. 101 



the various subgenera and species, though the value of this character 

 seems never to have been noticed by any previous writer in connexion 

 with the arrangement of the Sigmodont Muridae. 



The following Table gives the number of mammse found in a fe^v 

 of the best-known Sigmodontes not included in the present col- 

 lection : — 



Pectoral 



pairs of 



mammre. 

 Ochetodon mesicauus, Be Sauss. ... 1 

 Hesperomys (Ehipidomys) siimi- 



cbrasti, Z>e &«MS. 



H. (Vesperimiis)leucopus, i?rt/. ... 1 

 H. (V.) michigauensis,^i««^. ij- Bach. 1 



H. (Oryzomys) coiiesi, Alsf 2 



H. (Oalomys) bimaculatus, Watcrh. 2 

 Sigmodon bispidus. Say ^- Ord , . . 3 



We thus see that the number of mammae gives us an additional 

 character by which to separate Dr. Coues's subgenus " Vesperimus " 

 from Calomys, the first having only 3, while the latter has 4 pairs. 

 Sigmodon also, on whose generic distinction Dr. Coues has cast some 

 doubt ', is, so far as its mammae are concerned, very distinct from 

 any of the other New-world Muridae in having no less than .t pairs, 

 the largest number found in this group. 



1. Lepus brasiliensis, L. 



a (juv.). Cutervo, 9000', Feb. or Mar. 1879. 



2. EcHiNOMYs SEMisPiNOSus, Tomcs, p. Z. S. 18G0, p. 265. 

 a. (S (imm.), Tumbez, sea-level, June 1876. 



" In the reeds {Canna brava) on the banks of the river." 



[MUS MUSCULUS, L. 



a. Callacate, 4800', April 1879. 



This specimen had a large ffis^nw-larva in the flesh just above 

 the root of the tail (See C. 0. Waterhouse, Proc. Ent. Soc. 1881, 

 p. xxii).] 



3. HoLOCHiLUS (Nectomys) apicalis, Peters, Abhandl. Akad. 

 Berl. 1860, p. 152. 



Hesp. cephalotes, Desm., Tomes, P. Z.S. 1858, p. 548 (nee Desm.). 



a. Chirimoto, 5400', Jan. 1880. 



b. Huambo, 3700', April or May 1880. 



c. d (juv.). Tambillo, 5800', Feb. 1878. 



Dimensions, in inches : — 



Head and 



body. Tail. Hind foot. 



a. 6 ■■ 7-^ 9-0 1-96 



b. 6.. 8-4 lO'l 2-05 



In the paper quoted above, Prof. Peters described a large Guaya- 

 1 Mon. N. Am. Rod. p. 32, 1877. 



