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Show 450 MR. O. THOMAS ON A C O L L E C T I O N O F [June 17, HABROTHRIX, Waterhouse.-Form arvicoline ; tail short, thinly hairy ; fur generally long and soft ; ears and feet short; soles naked; thumb with a nail; mammae 2-2 = 8; interdental palate-ridges 4. Skull with long facial portion, very small interparietal, rounded supraorbital margins, and long palatine foramina. Teeth with high conical crowns, the folds in which soon wear out, leaving a simple indented outline. Species:-II. longipilis, Waterh., II. olivaceus, Waterh., H. xan-thorhinus, Waterh., &c, &c, about 20 in number. Range. Patrigonian Subregion ; northwards on the west to Ecuador, and on the east to South Brazil. OXYMYCTERUS, Waterhouse.-Like Habrothrix, but with a nail instead of a claw on the thumb, and with an elongated muzzle. Anterior plate scarcely developed, its edge slanting. Species:-H. nasutus, Waterh. (type), IT. hispidus, Pict., H. rufus, Desm., &c. Bange. South-Brazilian Subregion. Megalomys, Trouess.1, founded on II. pilorides, Pall., seems to me to fall within the genus Holochilus, Bdt., and not to be a true Hesperomys at all. Tylomys, Peters (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 plate of the zygoma-root, the outer wall of the foramen being absolutely cut back instead of projecting forwards. The remarkable supraorbital ledges are also quite unique. (See Peters's figures, M B . Ak. Berl. 1866, p. 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 Fesperimus extends down as far south as Peru, since it contains the two species H. cinereus and H. taczanowskii, formerly placed by me with much doubt in Bhipidomys, but which I now think must either be referred to Fesperimus or be made the types of a new subgenus, a course which I am unwilling to adopt without absolute necessity. With regard to the geographical aspect of M . Jelski'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 latimanus, pyrrhorhinus, taczanowskii, and albigularis, and the appearance of such Chilian and Patagonian forms as Bheithrodonpictus, H. scalops, II. xanthorhinus, 1 • Le Xahmdisto/ 1881, p. 3.r>7. |