258 PROCEEDINGS OF THE ACADEMY OF [1894. 



Measurements. — Total length, 197mm,; tail vertebne, 114; bind 

 foot, 22. Skull — Total length, 26*2; basilar length, 19; zygomatic 

 width, 12-7; length of nasals, 9*2; incisors to post-palatal notch, 10; 

 length of mandible 13-1; greatest width of mandible, 6-1. 



Four specimens of this race were taken on the foothills of the San 

 Bernardino Range at the entrance to Cajon Pass connecting the San 

 Bernardino Valley with the Mohave Desert. They represent the 

 dark mountain form of herro)d, the latter being typical of the low- 

 lands. The four specimens are remarkably uniform in all the 

 characters given. 



4. Sitomys keeni sp. nov. Type, No. 768, ad. J, Coll. S. N. Eboads. Mas- 

 set, Queen C'luirlotte Is., B. V., 1892. Col. by Eev. J. H. Keen. 



Description. — Size larger than S. americanus austents, ears 

 smaller, feet much larger, tail more than the length of head and 

 body. Colors above, uniform grizzled blackish- brown lacking the 

 darker dorsal area so prominent in austeriis. Feet and lower parts 

 ashy-white, abruptly defined against dark upper colors. Ears, 

 upper half of tail, and ring around eyes, sooty black. Fur dense 

 and short, this character and the colors of upper parts giving it an 

 Arvicoline cast. Skull large for size of body. Brain case relatively 

 very large, deep, and rounded, inflated behind above plane of 

 the orbits as the skull rests on a horizontal surface, so there is a 

 decided descent from a point just anterior to the parietals toward the 

 nasal bones, and a depression at the interorbital constriction. In all. 

 other forms examined this horizontal elevation of the parietals is not 

 greater than that of the frontals between the orbits, and is often less. 

 The nasals are short, double- pointed, and broadly wedged posteriorly 

 and not reaching behind the naso-preniaxillary processes. The an- 

 terior zygomatic width is much narrower than the squamosal, and the 

 antorbital foramina are thereby much contracted, giving the skull a 

 more tapering, triangular contour than in allied forms. The ratio 

 of squamosal-zygomatic breadth to total length in keeni, expressed in 

 millimeters, is 14 "3 to 26*3, in austerus 12-5 to 25. In keeni the 

 greatest parietal breadth is 12-5, in austerus 11. 



Measurements. (From spii'it specimen.) — Total length, 170 mm; 

 tail vertebrre, 88; hind foot, 24; ear, from crown, 10*5. Skull — 

 Total length, 26 -3; basilar length, 20 '5; zygomatic width, 14-3; 

 length of nasals 10-2; incisors to post-palatal notch, 11-3; length of 

 mandible, 14; greatest width of mandible, 6*3. 



