452 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



Counties, Texas; west to the Pecos Kiver; southeast to Rockport 

 and Nueces Bay, Texas; south to Victoria, TamauUpas. Lower 

 Sonoran Zone. 



General characters. — Size large; colors dull; ears larger than in any 

 other subspecies of leucogaster. In general most Hke hreviauritus, 

 but much less briglitly colored, lighter and grayer; with longer tail 

 and feet and much larger ears. 



Color.— Adult in winter (21180, Fort Clark, Texas, December 29): 

 Upperparts drab, darkest on middle of back; finely lined with darker 

 brow^iish, and with a wash of pale cinnamon over lower back and 

 hips; an indistinct stripe of cinnamon along sides between color of 

 upperparts and white of underparts, from fore legs to base of tail; a 

 blackish spot each side of nose at base of whiskers; ear tufts scant, 

 pale cinnamon color. Tail brown above with white tip; whitish 

 below, not sharply bicolor. Underparts white, the hairs of throat 

 and fore legs white to bases. There is Httle difference in the color of 

 adults at any season. Juvenile (3863, Amer. Mus. Nat. Hist., Corpus 

 Christi, Texas, April 24) : Above brownish-gray, close to mouse-gray, 

 finely fined with darker; sides paler. 



Sicull and teeth.— The skuU of longipes resembles that of hreviauri- 

 tus and differs from the skulls of arcticeps, melanophrys, and other 

 forms of leucogaster in being narrower and comparatively long, with 

 longer, higher braincase. Teeth relatively small. (Plate 15.) 



Measurements. — Averages and extremes of 12 adult specimens from 

 Texas and Tamaufipas: Total length, 166 (152-190) millimeters; tail 

 vertebrse, 55 (48-61); hind foot, 22.9 (22.0-25.0); ear from notch in dry 

 skin, 16.1 (15.0-16.9). Skufi: Condylobasal length, 27.1 (25.9-28.9); 

 zygomatic breadth, 15.1 (14.3-15.5); interorbital breadth, 4.7 (4.5- 

 5.2); breadth of braincase, 12.7 (11.9-13.3); length of nasals, 11.8 

 (10.9-12.7); length of mandible, 15.9 (15.1-17.1); maxillary tooth 

 row, 4.4 (4.1-4.8). For detailed measurements of specimens see 

 page 479. 



Type-specimen.— No. 186478, United States National :Museum. 

 Skin and skuU of young adult female (teeth Httle worn and basal 

 suture not entirely closed). CoUected March 11, 1887, by WiUiam 

 Lloyd. Merriam coUection, No. fffl. 



Remarlcs. — This subspecies exhibits less variation in pelage from 

 age and season than any other form of Onychomys. From lack of 

 specimens between their ranges as mapped, intergradation with the 

 Oklalioma form is not proved, but from the close resemblance between 

 the two forms it seems most certain, and the Oklahoma form cer- 

 tainly intergi-ades with arcticeps. There are so few good specimens 

 from the lower Pecos Valley that the actual relationship between 

 longipes and arcticeps at this point can not be determined, but it 

 seems most certain from the color of such skins as are available that 



