OCR Text |
Show 108 MR. O. THOMAS ON RODENTS FROM PERU. [Jan. 17, Mammae 4 or 6. Skull with more or less well-marked supraorbital ridges. The most peculiar member of the subgenus is H. sumichrasti, De Sauss.1, upon which both that author's Nyctomys and Tomes's Myoxomys'1 were founded3. These names must, however, both stand as synonyms of Rhipidomys, Tschudi, H. leucodactylus certainly belonging to the same subgenus as H. sumichrasti4. It is true that whereas the ordinary S. American Rhipidomyes are distinguished from true Hesperomys by having only 6 mammae, H. sumichrasti outdoes them all in this respect by having only 45, and in other ways is the most markedly specialized of them all; but nevertheless the difference is only in degree, and not in kind, so that I think we are justified in amalgamating Nyctomys with Rhipidomys as but one subgenus. There are, however, in addition to the well-marked species already referred to, three at least which, while they possess in different degrees some of the essential characters of Rhipidomys, yet are more or less intermediate between the true Hesperomys and the most typical members of this subgenus. The first of these is H. bicolor, Tomes6, the position of which, however, I caunot properly determine, not having seen a specimen. The other two are those next following, both new to science, of which H. taczanowskii would seem to be most nearly allied to Rhipidomys, notwithstanding its rounded supraorbital margin and untufted tail, and H. cinereus the least, having, in addition to these two last-mentioned characters, feet proportionally longer, with less Rhipidomyine foot-pads, and a more or less bicolor tail. Notwithstanding these differences, however, I prefer for the present to call these both Rhipidomys, as they have only three pairs of mammae, a number characteristic of the ordinary members of that group. 10. H. (RHIPIDOMYS) CINEREUS, sp. n. (Plate IV.) a. Cutervo, 9200', February or March 1879. Head and Forearm Ear-conch, Muzzle body7. Tail. Hind foot, and hand. length. to ear. fl. 2 •• 4*75 5*0 1*14 1*38 *64 1*18 Skull-dimensions. Back of Breadth of con- Total Greatest Molar incisors to striction between Lower jaw lengtb. breadth, series. 1st molar. orbits. (bone only). fl. .. 1*3 -73 -22 -37 '19 78 1 Eev. et Mag. Zool. 1860, p. 107. a P. Z. S. 1861, p. 284. 3 See Alston, Biol. Cent.-Am., M a m m . p. 143, 1880. 4 Mr. Tomes himself, when first describing Myoxomys, placed in it, besides H. sumichrasti (its type and most typical species), //. latimanus, Tomes ( = H. leucodactylus), and H. bicolor, Tomes. 5 See above, p. 101. 8 P. Z. S. I860, p. 117. 7 These measurements were taken before tbe skull was extracted. |