. Mammals of the Mexican boundary of the United States : a descriptive catalogue of the species of mammals occurring in that region; with a general summary of the natural history, and a list of trees . Mammals; Mammals; Trees; Trees; Natural history; Natural history. 382 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. head and body, 53 mm.; tail vertebrae, 32; hind foot, without claw, 13; ear above crown, 5. Skull, 18 by 10. Coloration somewhat similar to that of Mus musculus, but without the salmon tint beneath. The upper surface is brownish gray and the under parts grayish white. The tail is sca


. Mammals of the Mexican boundary of the United States : a descriptive catalogue of the species of mammals occurring in that region; with a general summary of the natural history, and a list of trees . Mammals; Mammals; Trees; Trees; Natural history; Natural history. 382 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. head and body, 53 mm.; tail vertebrae, 32; hind foot, without claw, 13; ear above crown, 5. Skull, 18 by 10. Coloration somewhat similar to that of Mus musculus, but without the salmon tint beneath. The upper surface is brownish gray and the under parts grayish white. The tail is scantily haired, and not distinctly bicolor. Cranial and dental characters.—In addition to the generic charac- ters pointed out by Dr. F. W. True," the dentition is also pecuUar. The niolar tubercles are paired, though not always exactly opposite. As they are ground down with wear, the enamel pattern of the grinding surfaces assumes almost a lozenge shape (fig. 68). The skull also has an unusual shape, which is shown in fig. a b c Fig. 09.—Baiomys taylori. • Skull, a, dorsal view; 6, ventral view; c, lateral view. Genus PEROMYSCUS Gloger (1841). Perorriyscus Glooer, Hand- u. Hilfsbuch d. Naturgesch., I, 1841, pp. xxx, 95. Type.—Peromyscus arboreus Gloger { = Mus sylvaticus noveioracen- sis Fischer). Characters.—Form slender; tail not shorter than body without head; ears large; claws weak; hind legs and feet long, the latter with six conical tubercles; soles naked or less than half hairy; skull with upper margin of orbit sharp, but without a bead; mandible with coronoid process short; dental tubercles low. SYNOPTICAL KEY TO THE SPECIES AND SUBSPECIES OF PEKOMYSCUS FOUND ON THE MEXICAN BOUNDARY LINE. a. Tail longer than head and body. b. Two front upper molars without subsidiary cusps or "corresponding enamel loops; soles of feet naked to the heel; tail nearly naked at base, without a distinct brush at the tip. c. Length more than 220 ram Peromyscus califomi


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