1 10 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 Rhipi- 

 domys. Fifth hind toes as in^. c'mereus. Mammse 6, one pectoral 

 and two inguinal pairs. Ears without a projection on their anterior 

 edge. Incisors and supraorbital margins as in U. cinereus. 



I have much pleasure in naming this peculiar species after Prof. 

 Taczanowski, to whose kindness I am indebted for the opportunity 

 of working out this interesting collection of mammals. H. tacz- 

 anowskii may be readily distinguished from the last species by its 

 much smaller size, and from its other near ally, H. bieolor, Tomes, 

 by the fact that that species has a much shorter tail (S'o in.), shorter 

 hair, and a pure white belly. 



12. Hesperomys (Habrothrix) olivaceus, Waterh. 



Mus {Habrothrix) o/i«ace««,Waterh. P. Z.S. 1837, p. 6. 

 Hesperomys renygeri, Waterh. Zool. Voy. Beagle, ii. p. 57, phxv. 

 (1839). 



a, b. Tumbez, sea-level, June 1876. 

 c. Callacate, 4800', April 1879. 



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 Mr. Dar- 

 win during the voyage of the ' Beagle.' Mr. Tomes also records it 

 from Ecuador. 



It will seen by the dimensions given above that the Callacate spe- 

 cimen 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-f. Huambo, 3700', April and May 1880. 



