422 Mr. O. Thomas on Hesperorajs pjrrliorhinus. 



Although these specimens of H. pyrrhorhinus are much too 

 young for me to draw up a full account of the species 

 from them, I am yet able to make out that it is certainly a 

 member of the subgenus Oryzoviys^ to which the great mass 

 of Brazilian Vesper-mice also belong. It has rounded hairy 

 ears, without projections, eight mammte, five interdental 

 palate-ridges, and naked soles with elongated posterior foot- 

 pads. Its molars are of the usual Oryzomys pattern, and the 

 length of m.^, which I have had to extract from below the 

 gum, is 2*6 millim. ; and therefore, judging roughly by this, 

 the only exact and unchanging measurement available on 

 such young specimens, the species is probably, when fully 

 grown, of about the size of H. ratticeps^ Hens.* 



The true H. pyrrhorhinus being thus an Oryzomys, M. 

 Stolzmann's Peruvian specimens, although possessing a cer- 

 tain superficial resemblance in size and colour to it, really 

 differ very materially in their essential characters, and I am 

 therefore driven to find a new name for them, there being 

 apparently no other described species to which they can be 

 assigned. 



Of the new species, for which I would propose the name of 

 H. lyyrrhonotusy no further description of the external charac- 

 ters is necessary beyond that already published f ; but it may 

 be interesting to note the chief characteristics of its skull. 

 These show it to belong, not to Rhipidomys, but to the small 

 group of Peruvian species to which Dr. Coues J has applied 

 the name of lliomasomys, although I should have preferred 

 to regard them as aberrant members of Vesjierimus^ to which 

 group I attached them in 1884 §. The skull, as a whole, 

 resembles that of //. cinereus^ Thos. ||, both in size and 

 general form. The muzzle is long and slender; the supra- 

 orbital space is narrow and parallel-sided, and its edges 

 square, but smooth and unbeaded ; the fronto-parietal sutures 

 meet at a sharp angle in the middle line ; the anterior edge of 

 the zygoma-root is vertical and without a projecting plate j 

 the palatine foramina are long and widely open ; the bullae 

 are most unusually large and swollen, exceeding those of any 

 other member of the genus that I have seen. The incisors 

 are very broad and strong, and their anterior surfaces are dark 

 orange, the lower ones being but slightly lighter than the 

 upper; the molars are of the usual pattern, but are much 



* Abhandl. Ak. Berl, 1872, p. 36. 



t P. Z. S. 1882, p. 107. X Am. Nat. xnii. p. 1275. 



§ P. Z. S. 1884, p. 449. 



II Figured P. Z. S, 1884, pi. xliv. figs. 2-4. 



