1898.] 



NATURAL SCIENCES OF PHILADELPHIA. 



3G9 



ASCHIZOMYS gen. nov. (Microtince). 

 Type, Aschizomys lemminus sp. nov. 



Generic characters. — Skull (fig. 1) broad, depressed, lightly built, 

 smooth and rounded. Palate as in true Evotomys. 1 Molars small 

 and weak, their angles rounded as in Evotomys (fig. 2), but the teeth 

 growing from a persistent pulp as in Microtus (fig. 3). Lower 

 incisor with long root (nearly as in Microtus) 

 which strongly displaces root of large poste- 

 rior lower molar (fig. 4). Form lemming- 

 like. Tail vertebra? shorter than hind foot • 

 pencil nearly as long as vertebrae. Plantar 

 tubercles six. Number of mammae unknown. 



Remarks. — As already intimated, the 

 proper disposition of this genus is open to 

 serious question. It must be recognized as 

 an intermediate between Evotomys and Mi- 

 crotus, but opinions may well vary between 

 the logical course of combining all three 

 under one generic name, and the convenient 

 expedient of allowing each to stand as a full 

 genus. For the present I have chosen the ™ 

 latter course. A third alternative would be tern of Aschizomys lem- 

 to remove from Microtus and unite w 7 ith mmus - (xlO). 

 Aschizomys the subgenera Eothenomys 2 and Anteliomys, 2 in which the 

 palate structure of Evotomys is exactly reproduced. With these 

 might be joined the highly aberrant Evotomys rufocanus. 3 This would 

 not only remove anomalous forms from Microtus and Evotomys, but 

 would also create a fairly homogeneous group characterized by the 

 combination of shelf-like palate with long-rooted lower incisor and 

 encapsulated posterior lower molar. When good material represent- 

 ing all these questionable forms can be brought together, some such 

 course as this may prove necessary. 



Aschizomys lemminus sp. nov. 



Type. — Adult, number ^^ United States National Museum, 

 collected at Kelsey Station, Plover Bay, Bering Strait, by C. W. 

 Baxter. 



•See North American Fauna, No. 12, fig. 7, and pi. II, fig. 10, July 23, 

 1896. 



'See North American Fauna, No. 12, pp. 45-49, pi. II, figs. 8 and 11. 

 3 For characters of Evotomys rufocanus see antea, p. 359-361 . 



