442 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



General characters. — Smallest of the subspecies of leucogaster, with 

 small hmd foot and short tail. Coloration darker than in arcticeps, 

 lighter than in Juscogriseus. 



Color. — Adult in fresh winter pelage (24897, Reese River, Nevada, 

 November 24): Upperparts rich glossy avellaneous, the face, head, 

 back, and rump darkened by streaking of the brownish hair tips; sides, 

 hips, and lower rump more cinnamon color; ear tufts pure white at 

 bases, buffy above; eai-s sharply marked dark brown and white; tail 

 grayish-brown above, with white tip. Entire xmderparts, including 

 whole of arms, hands, lower cheeks, imier sides of legs, and the feet 

 pure white. Adult in summer (23086, type, Blackfoot, Idaho, July 

 15): Like whiter specimens but faded, less glossy; the hair tips worn 

 away and the gray of underfur showmg through the worn pelage, 

 greatly modifying the general color. Ear tufts not noticeable and 

 color of ears greatly subdued. Juvenile (94668, Golconda, Nevada, 

 July 3) : Almost precisely like the young of 0. Z. arcticeps, but black 

 markings on ears more conspicuous. Immature (22996, Blackfoot, 

 Idaho, July 12): Like the juvenile but less ashy, more mouse gray; 

 the ear markings less conspicuous, the ear tufts whiter. 



Slcull and teeth. — Compared with skulls of missouriensis and 

 arcticeps, the skuU of hrevicaudus is short, flat, and comparatively 

 broad, with short and stout rostrum and much flattened brain case. 

 In size it averages less than skulls of any other subspecies of leuco- 

 gaster. The teeth are also slightly smaller than in the other races. 



Measurements. — Averages and extremes of 17 adults from Idaho, 

 Utah, and Nevada: Total length, 141 (130-155); tail vertebrae, 39 

 (31-42); hind foot, 19.1 (17-20); ear from notch m dry skin, 15.6 

 (14.4-16.7). Skull: Condylobasal length, 24.8 (23.8-26.0); zygo- 

 matic breadth, 14.3 (13.4-14.8); mterorbital breadth, 4.9 (4.7-5.1); 

 breadth of bramcase, 12.8 (12.3-13.3); length of nasals, 10.0 (9.4- 

 10.5); length of mandible, 14.4 (13.7-15.0); maxillary tooth row, 4.0 

 (3.8-4,2). For detailed measurements of specimens see page 475. 



Type-specimen. — ^No. ||-§|i, United States National Museum, 

 Biological Survey Collection. Skin and skull of adult male (teeth 

 much worn). Collected July 15, 1890, by Vernon Bailey and B. H. 

 Dutcher. Original number 1442. 



Remarlcs. — ^This is a small, weU marked subspecies, with a rather 

 extensive distribution in the Great Basin. It intergrades with 

 arcticeps in southwestern Wyoming, and with Juscogriseus all along 

 the northwestern border of its range. It is quite impossible to 

 determine many single specimens from the border line between the 

 distribution of fuscogriseus and hrevicaudus, but in the main the 

 hmits of the two subspecies have been well worked out. Juvenile 

 examples are especially helpful, as the color differences between the 

 two races are particularly developed in the young. 



