Ochrotomyini new tribe. Type genus—Ochrotomys Osgood, 1909. Definition—medium-sized semiarboreal muroid rodents with tail about equal to head-and-body (Packard, 1969); hindfoot short and broad, digit V nearly as long as II-IV, plantar pads large and close set; carotid circulation complete (character state 0 per Carleton, 1980); skull with amphoral interorbit and smooth braincase; zygomatic plate narrow, no formation of dorsal notch; tegmen tympani adnate to squamosal (Voss, 1993), alisphenoid strut present; molars more brachyodont than Peromyscus, enamel thick, accessory lophs(ids) well developed (Hooper, 1957); m3 slightly smaller than m2, enteroconid and posterolophid usually discrete elements; vertebral column with 13 thoracic and 6 lumbar vertebrae, 1st rib articulating 7th cervical and 1st thoracic (Carleton, 1980); humerus lacking entepicondylar foramen (Manville, 1961); three complete and four incomplete transverse palatal ridges (Carleton, 1980); gastric glandular epithelium somewhat reduced and incisura angularis moderately deep (Carleton, 1973), gall bladder absent (Carleton, 1980); preputial glands large, ampullary glands absent (Arata, 1964); baculum and phallus short and wide, spination pronounced, urethral process present, dorsal and ventral lappets lacking (Blair, 1942; Hooper, 1958); 2n=52, G-banding patterns highly derived (Engstrom and Bickham, 1982; Patton and Hsu, 1967). Contents—Ochrotomys Osgood, 1909.
Although named as a subgenus of Peromyscus, the distant kinship and generic segregation of Ochrotomys have been repeatedly sustained (Blair, 1942; Carleton, 1980; Hooper, 1958; Hooper and Musser, 1964b; Patton and Hsu, 1967). Informally grouped with "peromyscines" by Carleton (1980), but his own results (see Carleton, 1989:115), together with karyological and molecular studies (Engel et al., 1998; Engstrom and Bickham, 1982), suggest earlier origination within the neotomine radiation.