OCR Text |
Show 100 MR. O. THOMAS ON RODENTS FROM PERU. [Jail. 17, peromys now usually admitted. Of these Calomys claims four species, one being new ; Rhipidomys also four, of which two are new ; and Habrothrix the 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 a m 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 provisionally referred them. The chief previous information bearing on this subject is comprised in Tschudi's classical work on tbe fauna of Peru', and in M r . Tomes's papers on the Mammals collected in Ecuador by M r . Fraser. Of the 6 Muridae mentioned by Tschudi, only one, Hesperomys leucodactylus, was found by M . Stolzmann; 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, aud 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 m e with regard to the comparative lengths of the different parts of the alimentary canal5, because the intestines had been removed from all the specimens before they came into m y bauds. Of the new species obtained by Mons. Stolzmann, 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 Mus which possess spines in their fur, that I have always been surprised at there being no spiny members of such a large and variable tropical genus as Hesperomys. The present discovery of a spine-clad Vesper-mouse is therefore proportionately interesting. As in the Old-world Mus ', so here in Hesperomys, I find that the number of mammae is both very constant0 and very distinctive of J Pp. 177-184(1844) 2 P. Z. S. 1858, p. 546; 18(10, pp. 211 & 260. a P. Z. S. 1880, p. 696. 4 Infrii, p. 105. 5 See P. Z.S. 1881, p. 531, &c. 6 The variation in the number in some of the common species of Mus, viz. hi M. decvmanus, rattus, and alcxandrinus, bas caused this character to fall into disrepute among writers on Eodentia; but, with tbe exception of these species, and of one or two others which have tbe unusually large number of from 14 to 18 maminaB, I bave never, in any single instance, found a specimen of either Mus or Hesperomys in which tbe number differed from tbat normal to the species. I do not of course assert that individual variations do not occur, but only that they 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. |