1915.] 



THOMOMYS BOTM GROUP. 



57 



CTiaracters. — Size smaller than hottse. with the same small ears and 

 very similar colors in both winter and summer pelage; skull slenderer, 

 with shorter bullae and less projecting incisors; mammse in 4 pairs, 

 inguinal 2-2, pectoral 2-2. 



Color. — Wivier pelage: Upperparts dark ochraceous-tawny, dark- 

 ened above by black-tipped hairs; nose, cheeks, and ear patches 

 blackish; underparts lightly washed with rich ochraceous; tip of .tail, 

 hind feet, and lining of cheek pouches usually whitish. Summer 

 pelage: Lighter and suffused with tawny above and below. Young, 

 paler, more buffy above and whitish below. 



SlcuU. — Relatively narrower, slenderer, and less arched than that 

 of hottse; bullae shorter, more rounded; interparietal more quadrate; 

 external auditory meatus with less expanded rim. Dentition lighter; 

 incisors less projecting and more distinctly grooved. It differs from 

 fulvus, with which it was originally compared, in less spreading 

 zygomatic arches, slenderer rostrum, and relatively narrower brain- 

 case. 



Measurements. — Topotype ( c? ad.):^ Total length, 231; tail, 74; 

 hind foot, 30. Average of 5 typical males from San Jacinto Mountains : 

 232, 77, 30.2. Average of 5 females: 199, 65, 27.4. SMll (of topo- 

 type, c? ad.): 2 Basal length, 34.5; nasals, 13.5; zygomatic breadth, 

 23; mastoid breadth, 18; interorbital breadth, 6.5; alveolar length of 

 upper molar series, 7.5. 



Remarlcs. — From hottx, nigricans differs in lighter, slenderer skuU; 

 more abruptly decurved and more distinctly grooved incisors; lighter 

 dentition; and numerous details of cranial and external characters; 

 but scarcely if at all in color. It is much smaller and darker than 

 pallescens with which it intergrades at Elsinore and Wildomar, 

 while Twin Oak specimens are clearly intermediate between nigricans 

 and hottse. 



In a series of 18 specimens from Santo Tomas, Lower California, I 

 find no characters by which to recognize TJiomomys apJirastus as even 

 subspecifically different from nigricans. A series of 32 specimens of 

 alticolus from the Victoria Mountains, farther south on the peninsula, 

 are scarcely distinguishable from nigricans in external characters, but 

 in cranial characters tend toward anitx. 



Specimens examined. — Total number, 401, as follows: 



California (southern): Ballena, 1; Campo (San Diego County, at 2,500 feet alti- 

 tude), 8; Cuyamaca Mountains, 16; Dulzura, 14; Escondido, 3; Foster, 5; 

 Fullers Mill, 1; Grapevine Spring, 1; Hemet Valley, 5; Jacumba, 11; Jamul 

 Creek, 3; Julian, 15; Kenwortliy, 2; La Puerta, 24; Mountain Spring, 1; 

 Pine Mountains, 1; Poway, 1; Rose Canyon, 1; San Jacinto Mountains (south 

 end at 5,000 to 8,000 feet), 21; Santa Rosa Peak, 1; Santa Ysabel, 15; Schains 

 Ranch, 4; Strawberry Valley (in central part of San Jacinto range at 6,000 

 feet), 24; Thomas Mountain, 1; Tia Juana, 2; Tia Juana River (mouth), 1 

 Warners Pass, 7; Witch Creek (San Diego County at 2,750 feet), 53. 



iNo. 148685, U. S. Nat. Mus. 



2 No. 148688, U. S. Nat. Mus. 



