1894.] NATURAr. SCIENCES OF PHILADELPHIA. 257 



length, 18-8; zygomatic width, 13; length of nasals, 9-8; incisors to 

 post- palatal notch, 9-8; length of mandible, 12-8; greatest width of 

 mandible, (5. 



This mouse, of which I have received but one specimen among 

 a considerable sei'ies of manmials from the same region, is strikingly 

 different from any Sitomi/.'^ that I have seen or can find description 

 of It is not merely a desert form of some group already known, 

 but if more specimens prove its characters, as given above, to be 

 constant, it represents a section intermediate in character between 

 Oiu/cJiomiis and SItomi/g. Its relationships, however, are much closer 

 to Sitomys. In its six tuberculate hind feet, the elongate lower 

 molar, the prominent coronoid process, and proportionate length of 

 tail to body, insolatus is a B(iioiii;is,''\mt the trefoil character of its first 

 upper molar is in another direction. The subgenus Baiomys, sepa- 

 rated from Sttomijs almost solely on its well- developed coronoid and 

 short tail, is of very questionable value, as many ^Sitomijs show a 

 tendency to the first character which have very long tails while other 

 short-tailed species show the reverse. In fact a large series of 

 Sitomys amerlcanus from Pennsylvania and New Jersey, which I 

 have studied, show individual variations in these characters among 

 themselves, which suffice to very closely connect Baiomys with the 

 typical form. In case further material should show the dental 

 peculiarity of insolatus to be constant, I would propose that it be 

 placed in the subgenus Trinodoidonys (Subgen. nov.) with characters 

 as already given. 



3. Sitomys herroni nigellus subsp. nov. Type. No. 3,496, ad. J* , Coll. Acad. 

 Nat. Sci.. Phila. West ("ajon Pass, San Bernardino Mts., California, Jan. 

 11th, 1894. Col. by E. B. Herron. 



Description. — General characters as in Sitomys herroni,^ the buffy- 

 gray of that species being deeply lined and shaded in the subspecies 

 by a predominance of long black hairs, the blackish shade being 

 most pronounced across the posterior half of body. The pelage is 

 longer, denser, and more harsh than in herroni, the tail and ears 

 much darker, the buft' of sides and cheeks of herroni becoming in 

 nigellus deep fawn and the bufiy cast of belly purer white. Skull 

 as in herroni. 



- True, Proc. Nat. Mas. XVI, 7.57. 

 3 Ehoads, Amer. Nat., 1893, 832. 



18 



