VOL. XX, PP. 19-22 FEBRUARY 23, 1907 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



FOUR NEW POCKET MICE. 

 BY WILFRED H. OSGOOD. 



Collections recently made by Nelson and Goldman in Lower 

 California contain a wealth of material in the genus Perognathus 

 which has been submitted to the writer for study. The greater 

 part of this material is referable to described forms, the known 

 ranges of which in many cases are thus greatly extended. Three 

 forms appear, however, which need to be characterized, two of 

 them subspecies of P. penicillatm and one of P. spinatus. A 

 fourth, also here described, is an apparently distinct species of 

 the subgenus Perognathus secured by Mr. Goldman during some 

 preliminary work on the east side of the Colorado River in 

 Arizona and Sonora. The types of these forms are in the Bio 

 logical Survey Collection. 



Perognathus bombycinus sp. nov. 



Type from Yuma, Arizona, No. 136,123 U. S. National Museum, Biologi 

 cal Survey Collection. cT adult. March 18, 1905. E. A. Goldman. 



Characters. Size, color, and general appearance as in P. p. bangsi ; skull 

 with large, full mastoids and small, nearly square interparietal. 



Color. As in P. p. bangsi; upperparts pale vinaceous buff, lightly lined 

 with dusky ; ears edged with whitish, a well developed white spot at an 

 terior base ; underparts white. 



Skull. A miniature of that of P. ampins; size as in P. p. bangsi; mas 

 toids very large and full ; parietal border of mastoid with a marked angle 

 between interparietal and orbit ; interparietal small and compressed, trans 

 verse dimension less than longitudinal ; lower premolar larger than last 

 molar. 



Measurements. Type and two specimens from northwestern Sonora, re 

 spectively : Total length, 134, 140, 131 ; tail vertebrae, 79, 82, 77 ; hind foot, 

 18.5, 18.5, 18.5. Skull of type : Occipito-nasal length, 20.4 ; basilar length, 

 14.5; mastoid width, 11.7; zygomatic width, 9.8 ; interorbital constriction, 

 4.4; nasals, 7; interparietal, 2.5 x 2.7; diastema, 5.1; maxillary toothrow, 3. 



Remarks. No external difference appears between this species and P. p. 

 bangsi, but cranial distinctions are marked. No evidence of intergradation 

 between the two forms is shown by any specimens yet examined. Speci- 

 3 PROC. BIOL. Soc. WASH., VOL. XIX, 1907. (19) 



