1898.] 



NATURAL SCIENCES OF PHILADELPHIA. 



361 



root of the lower' incisor and the posterior lower molar, while not 

 typical of either genus are clearly suggestive of Microtus rather 

 than Evotomys. The palate structure, on the other hand, appears 

 to agree with that of Evotomys. The question of the animal's true 

 position cannot be answered until good series of specimens represent- 

 ing different ages are available for comparison. 



Evotomys wosnessenskii (Polyakoff). 



1839. ?? Arvicola rubricaius Richardson, Zoology of Beechey's Voyage of the 



Blossom, p. 7 (Bering Strait). 

 1881. Arvicola wosnessenskii Polyakoff, Appendix to Volume XXXIX of 



the Memoirs of the St. Petersburg Academy of Sciences, p. 56 



(text in Russian) Kamtschatka. 

 1884. Arvicola wosnessenskii Lataste, Ann. Mus. Civ. di St. Nat di Genova,. 



XX, p. 28. 



Skull. — The skull of Evotomys ivos?ie$se7iskii as compared with 

 that of E. rutilus and E. alascensis is slightly narrower and more 

 depressed, though the differences in general form are not very strik- 

 ing. The anterior edges of the antorbital foramina are folded out- 

 ward so as to form conspicuous swellings, which for want of a bet- 

 ter name I have called rostral protuberances. These protuberances 

 are apparently formed by the wall of a canal which takes a super- 

 ficial downward course from the anterior edge of the antorbital for- 

 amen, and probably transmits a branch of the fifth nerve. In Evo- 

 tomys wosnessenskii the rostral protuberances stand further forward 

 from the bases of the zygomata than in E. alascensis (fig. 1). This 



position as well as their large size makes 

 them very conspicuous. Audital bulla? 

 small, much smaller than in E. rutilus or 

 E. alascensis, their greatest breadth about 

 equal to alveolar length of maxillary 

 tooth row. Mandible slender and lightly 

 built, with weaker articular process and 

 angular process than in the related species. 

 Measurements of an adult skull from 

 Bering Island : greatest length, 24 mm. ; 

 basal length, 22.8; basilar length, 21 ; zygo- 

 matic breadth, 13.6 ; mastoid breadth, 

 11; interorbital constriction, 4 ; nasals, 

 7.8 ; incisive foramen, 5 6 ; diastema, 7.4 ;, 

 maxillary molar series (alveoli), 5 ; man- 

 dible, 13.8 ; mandibular molar series (al- 

 veoli), 5. 



Fig. 1. Rostrum of Evo- 

 tomys wosnessenskii (upper 

 figure) and E. alascensis 

 (lower figure), (x 3f ). 



24 



