1894.] NATHRAL SCIENCES OF PHII>ADELPHIA. 283 



If the latter course be adopted, we still have an inexact diagnosis 

 to accommodate the three or four exceptional species which develop 

 the fifth triangle, and the name 3Iijiwme.% based by Rafinesque on a 

 five-triaugled species, becomes inapplicable. On this account, it 

 seems to me quite consistent with the exact subdivision of the other 

 members of the genus Arvkola, as well as necessary, that the sub- 

 genus Tefnonerodon be adopted. 



Arvicola (Tetrainerodon) tetramerus sp. nov. Type Xo. 3-27, ad., ^ , Coll. of 

 S. X. Ehoads, Beacon Hill Park, Victoria, British Columbia, Mav 19, 1892. 

 Coll. by S. X. R. 



Desen'ption. — Size medium, about the same as A. pe)insi/lvcmicus. 

 Tail rather long. Color above, grizzled blackish-brown, beneath 

 clear ash. Feet grayish-brown. Tail bicolor, matching corre- 

 sponding surfaces of body, well-haired and penicillate. 



Dentition as in Mi/novie.^, but lacking the posterior fifth section 

 of middle upj^er molar, typical of that subgenus. 



Measurements (of type). — Total length, 170 mm; tail vertebrae, 

 50; hind foot, 23. Average of five adults — Total, 175; tail, 48; 

 foot, 22. Skull — Total length, 26-5; basilar length, 24; zygomatic 

 breadth, 15; length of nasals, 7-5; incisors to post- palatal notch, 

 14-2; interorbital constriction, 3-4; length of mandible, 16; width 

 of mandible, 8-5. 



Ten specimens of this species were taken in the suburbs of Vic- 

 toria, in the dry, grassy woods of Beacon Hill Park, overlooking the 

 Strait of Fuca. 



They most nearly resemble townsendi from Puget Sound in essen- 

 tial characters. Compared with toivnseiidi the Victoria voles may 

 be readily distinguished by their much smaller size, blacker colora- 

 tion above, the greater relative width of the interorbital region, the 

 supraorbital ridges never meeting medially as in old towii.-tendl, and 

 the posterior margins of the frontals being rounded and but slightly 

 encroaching upon the parietals. This species differs essentially from 

 A. occidentalis and A. californicus as defined by Baird in its lack of 

 red or yellow tints. From A. montaiius Peale (fide Baird) tetramerus 

 differs in the greater relative length between the upper molars and 

 incisors, also in the posterior upper molar having four outer, salient 

 angles instead of three. Prof. Baird states there is a great similarity 

 between the colors of montanns and edax and that the former is 

 grayer than townsendi. In tetramerus the colors are much darker. 



