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NORTH AMERICAN FAUNA. 



[No. 12. 



nijp and plantar tubercles. Although this system leads to a tolerably 

 satisfactory arrangeraeut of the Europeau voles, it can not be applied 

 to the genus at large, since it would unite such distinct groups as 

 Arvieola and ChlJotus, or Keojiher and Pitymi/s. Lataste's classification 

 is as follows : 



Genus Microtus: ' 



Subgenus Jli/odes {rutilns, glareohis). 



Subgenus Microtus {gregalis. arralis, agresiis, raiticeps, pcnnsylvanicns, nivalis)' 

 Subgenus Arvicola {ierresiris, musignani). 



Subgenus Pitymys (pinetoruni suhierraneus, socialis, middendorffi). 

 Subgenus Lasiopodomys (hrandti). 



The subgenera Myodes and Lasiopodomijs are equal, respectively, to 

 the genus Evoiomijs and the subgenus Phaiomys of the present i)aper. 

 The subgenera Microtm and Arvicola coincide with groups here recog- 

 nized under the same names, while the subgenus Pitymys is essentially 

 the same as that defined on page 58. Lataste, however, includes in 

 Pitymys the species middendor-ffii, which is probably not a member of 

 that group as now understood. 



CHARACTERS ON WHICH THE PRESENT CLASSIFICATION OF THE 

 SUBGENERA OF MICROTUS IS BASED. 



In the discussion of the systems of classification hitherto adopted, 

 the impracticability of subdividing the genus Microtus according to 

 the variations in any one set of characters has been shown. The 

 highly artificial systems of Blasius and Lataste give the best examples 

 of the unnatural results to which any such course must inevitably lead. 

 In the present paper the classification used is based on an assemblage 

 of characters. The more important of these, or the ones least adapted 

 to the special needs of the different animals, and hence least likely to 

 vary, are: Form of skull, structure of bony palate, pattern of enamel 

 folding, number of mammoe, number of plantar tubercles, and presence 

 or absence of musk glands on the sides. Characters of less importance, 

 because more readily modified to fit a species to the special requirements 

 of its environment, and hence more unstable, are: Qualitj^of fur, hair- 

 iness of soles, length of tail, form of front feet, size of eyes, and form 

 of external ear. It is only through careful consideration of all these 

 tliat a satisfactory arrangement of the species can be obtained. 



Xearlj' all of the characters now used have been recognized in classi- 

 fications already proposed. In eyery case, however, they have been 

 assigned degrees of importance different from those which the^^ now 

 receive. To take the three most conspicuous examples: De Selys 

 Longchamps arranged the voles with regard to their external form; 



qui portent sur les extremites mal definies et eminemment variables, soit i^osterieur 

 dc la derniere molaire superieure, soit anterieur de la premiere molaire inferieure.'' 

 (Ann. del Mus. Civ. di Geneva, Ser. 2a, Vol. IV, p. 260 footnote.) 



Compare with this the opinion expressed by Biieliner. (See footnote, p. 25.) 



^ To Lataste is due the credit of recognizing the true status of the name Microtus. 



