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Show 110 MR. O.THOMAS ON RODENTS FROM PERU. [Jan. 17, above and beneath, uniformly thinly clad with brown hairs. Feet white, with a faint admixture of brown on the metacarpus and metatarsus. Foot-pads large and rounded, as in the typical Rhipidomys. Fifth hind toes as in II. cinereus. M a m m a e 6, one pectoral and two inguinal pairs. Ears without a projection on their anterior edge. Incisors and supraorbital margins as in H. cinereus. I have much pleasure in naming this peculiar species after Prof. Taczanowski, to whose kindness I a m indebted for the opportunity of working out this interesting collection of mammals. //. taczanowskii m a y be readily distinguished from the last species by its much smaller size, and from its other near ally, IL bicolor, Tomes, by the fact that that species has a much shorter tail (3*5 in.), shorter hair, and a pure white belly. 12. HESPEROMYS (HABROTHRIX) OLIVACEUS, Waterh. Mus (Habrothrix) olivaceus,W&terh. P. Z.S. 1837, p. 6. Hesperomys renggeri, Waterh. Zool. Voy. Beagle, ii. p. 57, pl.xv. (1839). A, b. Tumbez, sea-level, June 1876. c. Callacate, 4800', April 1879. Head and body. a.cS 3*7 6.o*(imm.) 3*0 c 2 . • •. 3*8 Tail. 3*14 2*75 2*65 Hind foot. •87 •86 •79 Forearm and hand. 1*05 1-0 1-0 Muzzle to ear. •93 •86 •94 Ear-conch. length. •63 •00 •56 This species seems to be a very common one all along the western parts of S. America ; for, in addition to these Peruvian examples, the Museum contains a considerable series of specimens from Bolivia and Chili, including the types of the species, collected by M r . Darwin during the voyage of the ' Beagle.' Mr. Tomes also records it from Ecuador. It will seen by the dimensions given above that the Callacate specimen has somewhat shorter ears, feet, and tail than the others, while it has a larger body and head ; and it has also rather thicker and softer fur. It seems very probable, however, that these differences are only owing to the much greater altitude at which it was obtained, since it is a well-known law among mammals that individuals from colder climates have a tendency to have larger bodies and shorter extremities than those of the same species living in warmer places. 13. HESPEROMYS (HABROTHRIX) CALIGINOSUS, Tomes, P. Z. S. 1860, p. 263. a-/. Huambo, 3700', April and May 1880. a. 6". b.d . c2. Head and body. . 4*0 . 3*9 . 3-5 Tail. 2-9 3-01 3-0 Hind foot. '84 •85 85 Forearm Ear-conch, and hand, length. 1-07 '52 - -51 1-05 -52 Muzzle to ear. •96 •98 •92 |