100 MR. O. THOMAS ON RODENTS FROM PERU. [Jan. 1/, 



2i€roinys uo\¥ usually admitted. Of these Calomys claims four species, 

 one being new ; Bhipidotmjs also four, of wliich two are new ; and 

 Habrothrix tlie remaining two, both of which are previously-known 

 species. There are thus three new species in the collection ;■ and of 

 two of the others I am somewhat doubtful of the determination ; so 

 that I think it possible that either or both of them will in the end 

 turn out to be really different from the species to which I have pro- 

 visionally referred them. 



The chief previous information bearing on tliis subject is comprised 

 in Tschndi's classical work on the fauna of Peru', and in ^Ir. Tomes's 

 papers on the Mammals collected in Ecuador by iNIr. Fraser". 



Of the 6 Muridee mentioned by Tschudi, only one, Hesperomys 

 lencodactylus, was found by M. Stolzmanu ; while of the 13 brought 

 from Ecuador by Mr. Fraser he obtained six, or just about half; so 

 that from his well-preserved spirit-specimens I have been able to 

 supplement the descriptions given by Mr. Tomes, many of which 

 were drawn up only from skins. 



It is perhaps well to mention that, when describing these Rats and 

 Mice, I found it possible, owing to their excellent state of preservation, 

 entirely to dry the hairs, so that the colour and texture of the fur, 

 and the general appearance of the animals were just as they 

 would have been if the specimen had been examined when recently 

 killed. I have been unfortunately unable to supplement from this 

 collection the notes recently published by me with regard to the 

 comj)arative lengths of the different parts of the alimentary canal\ 

 because the intestines had been removed from all the specimens 

 before they came into my hands. 



Of the new species obtained by Mous. Stolzmanu, H. spinosus* is 

 perhaps the most interesting, as being the first Hesperomys that has 

 been found with spiny fur. I have long expected that such a form 

 would be discovered. There are so many examples of tropical 

 species of the neighbouring genus Mtis which possess spines iu their 

 fur, that I have always been surprised at there being no spiny 

 members of such a large and variable tropical genus as Hespieromys. 

 The present discovery of a spine-clad Vesper-mouse is therefore pro- 

 poitionately interesting. 



As in the Old-world Mvs '\ so here in Hespteromys, I find that 

 the number oi mammse is both very constant^ and very distinctive of 



J Pp. 177-184 (1844) 



= P. Z. S. 1858, p. 546; 1860, pp. 211 & 260. 



3 P. Z. S. 1880, p. 696. 



" Lifra, p. 105. 



« SeeP.Z.S. 1881, p.531, &c. 



^ The variatiou iu the number iu some of the commou species of Mtis, tjz. in 

 iV. decvr/iamis, rattv.s, and alcaandrinus, has caused this character to fall iuto 

 disrepute among writers on Eodentiii; but, with the exception of these species, and 

 of one or two others which have the unusually large niunber of from 14 to 18 

 mammse, I hare never, in any single instance, found a specimen of either Mtis 

 or Hespcrciirijs in which the number differed from that normal to the species. 

 I do not of course assert that individual variations do not occur, but only that 

 tbey must be extremely rare, as I have never met with any in all the large series 

 of specimens that I have examined with special reference to this point. 



