450 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



ONYCHOMYS LEITCOGASTER CAPITULATUS Holllster. 



1913. Onychoviys leucogaster capitulatm Hollister, Proc. Biol. Sbc. Washington, 

 vol. 26, p. 215. December 20. 



Type-locality. — Lower end of Prospect Valley, 4,500 feet, Hualpai 

 Indian Reservation, Grand Canyon, Arizona. 



Geographic distribution. — Known only from the type-locality and 

 from Aubrey Valley, Arizona. 



General characters. — Darker than melanophrys; lighter, more red- 

 dish-brown, than fuliginosus. Coloration much like that of ruidosse, 

 but slightly smaller in size and mth considerably smaller and weaker 

 skull. 



Color. — The coloration of this form, in all pelages, closely resembles 

 that of 0. I. ruidosse. 



STiull. — Like skulls of ruidosse and melanophrys, but smaller and 

 generally weaker, vnth lighter rostrum, narrower interpterygoid space, 

 and smaller audital bullae. (Plate 15.) 



Measurements. — Type and averages of 10 adults from vicinity of 

 type-locality, the latter in parentheses: Total length, 142 (147); tail 

 vertebrae, 43 (44); hind foot, 21.0 (21.9); ear from notch in dry skin, 

 14.6 (14.8). Skull: Condylobasal length, 25.1 (25.1); zygomatic 

 breadth, 14.0 (14.0) ; interorbital breadth, 4.7 (4.6) ; breadth of brain- 

 case, 13.0 (12.6); length of nasals, 10.9 (10.9); length of mandible, 

 14.5 (14.5); maxillaiy tooth row, 4.3 (4.3). For detailed measure- 

 ments of specimens, see page 478. 



Type-specimen. — No. 202612, United States National Museum, 

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

 moderately worn) in fresh fall pelage. Collected September 26, 1913, 

 by Edward A. Goldman. Original number, 22234. 



Remarks. — Tliis form is closely related to 0. I. ruidosse, but the 

 slightly smaller size, smaller ear, and uniformly smaller and weaker 

 skull, characters so constant in the series of 20 specimens as to 

 appear truly reHable, make it necessary to recognize it by name. No 

 Onychomys was known from the region before this series was taken 

 by Mr. Goldman in 1913, and the type-locahty is the most westerly 

 point of the known range of the leucogaster group in the Southwest. 



Specimens examined. — Total number, 20, from locahties as follows: 



Arizona: Aubrey Valley, 10 miles south of Pine Spring, 6; Grand 

 Canyon, Hualpai Indian Reservation, 14. 



ONYCHOMYS LEITCOGASTER ALBESCENS Merrlam. 

 1904. Onychomys leucogaster albescens Merriam, Proc. Biol. Soc. Washington, 

 vol. 17, p. 124. June 9. 



Type-locality. — Samalayuca, Cliihuahua, Mexico. 



Geographic distribution. — Known only from the sand dunes at the 

 type-locality in northern Chihuahua, and from Monument No. 1, 

 Mexican boundary Hne, opposite El Paso, Texas. 



