450 MR. O. THOMAS ON A COLLECTION OF [Juiie 17, 



Habrothrix, Waterhouse. — Form arvicoline ; tail short, thinly 

 hairy ; fur generally long and soft ; ears and feet short ; 

 soles naked ; thumb with a nail; maniniBe 2-2 = 8 ; inter- 

 dental palate-ridges -I. 



Skull with long facial portion, very small interparietal, 

 rounded supraorbital margins, and long palatine foramina. 



Teeth witli high conical crowns, the folds in wliich soon 

 wear out, leaving a simple indented outline. 

 Species: — II. longipilis, V/aterh., H. olivaceus, Waterh., H. xan- 



thorhinus, Waterh., &c., &c., about 20 in number. 

 liaiige. Pat.igoiiian Sabregion ; northwards on the west to 

 Ecuador, and on the east to South Brazil. 



Oxymycterls, Waterhouse. — Like Heibrothrix, but with a nail 

 instead of a claw on the thumb, and with an elongated muzzle. 

 Anterior plate scarcely developed, its edge slanting. 



Species : — //. nasutus, Waterli. (type), IT. hispidus, Pict., 

 H. rufus, Desm., &e. 



Ranye. South-Brazdinn Subregion. 



Megalomys, Trouess.', founded on H. pilorides. Pall., seems to 

 me to fall within the genus Holochilus, Bdt., and not to be a true 

 Hesperomys at all. 



Tylomys, Poters {Neomys, Gray), should, on the other hand, be 

 certainly allowed separate generic rank, chiefly on account of its very 

 peculiarly shaped infraorbital foramen, which is of the same breadth 

 above and below, and to which there is no projecting external 

 anterior ])late of the zygoma-root, the outer wall of tlie foramen being 

 absolutely cut bsick instead of projecting forwards. The remarkable 

 supraorbital ledges are also quite unique. (See Peters's figures, 

 MB. Ak. Berl. 1866, n. 404.) 



By the above arrangement it will be seen that the name Calomys 

 is restricted to the small group to which it was originally applied by 

 Waterhouse ; that Oryzomys, which hitherto was supposed to include 

 only two North- and Central-American species, really contains the 

 great mass of the South-American muriform Vesper-mice to which 

 Calomys has been commonly applied ; and that the range of Dr. 

 Coues's subgenus Vesperimvs extends down as far south as Peru, 

 since it contains the two species //. cinereus and H. taczanowsl'ii, for- 

 merly placed by me with much doubt in Rhipidornys, but which I 

 now think must either be referred to Vesperimus or be made the 

 types of a new subgenus, a course which 1 am unwilling to adopt 

 without absolute necessity. 



With regard to the geographical aspect of M. Jehki's collection 

 as compared with that of M. Stolzmann's, the more southern locality 

 of the former results in the dropping out of the Ecuadorean and 

 Amazonian species, such as Hesperomys laHmanus, pyrrhorhinus, 

 taczanowskii, and albiyularis, and tlie appearance of such Chilian and 

 Patagonian forms as Rkeithrodon pictus, //. scalops, H. xanthorhinus, 



' 'Le Xaturalistp,' 1881. p. .S.57. 



