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NORTH AMERICAN FAUNA. 



[Xo. 12. 



Westergren. The tracings of the enamel pattern of Microtus Inteus 

 and M. lagxirus are enlarged from tigs. 10, 11, 15, and 16 of PI. XIII of 

 Biiclmer's ' WissenscLaftliclie Resultate der von N. M. Przewalski iiach 

 Gentral-Asien unternommeiien Eeisen.' In fig. 22 tlie enamel patterns 

 of the front lower molar and middle and back upper molars are enlarged 

 from Mr. Hollick's pencil drawing of a s^jecimen from Fokien, China 

 (British Museum Eegister 92. 10. 12. 52), the other teeth from fig. 1, PI. 

 XLYI of Milne-Edwards's ' Eecljerches pour servir a 1' Histoire Xaturelle 

 des Mammiferes.' Fig. 23 is compounded in the same way from Mr. 

 Hollick's drawing and the original figure published by Thomas. 



THE SUBFAMILY MICROTIN^ AND ITS MAIN DIVISIONS. 



The subfamily Microtince^ is a group of murine rodents closelj^ related 

 to the Xeotomince, Cricetinoe^ and MyotaJpincv.^ It is distinguished from 

 the first and second by cranial and dental characters; from the last 

 chiefly by i)eculiarities in external form.^ While it is not the purpose 

 of the present paper to discuss the relationships of the Microtince to 

 any of these, it is important to consider in some detail the larger divisions 

 of the subfamily itself before taking up the genera and subgenera. 



The members of the subfamily Microtinw fall naturally into two 

 sui)er generic groups, the Lemmi and Microti^ or lemmings and voles. 

 The former includes the genera Syna^^tomys^ Lemmus^ and Dicrostonyx^ 

 the latter the genera Phenacomys^ JSvotomys, Microtus, and Fiber. 



Lemmi. — Skull generally broad and massive; lower incisors short, 

 with roots ending on inner side of molars (PI. Ill, fig. 1); crowns of 

 maxillary teeth scarcely, if at all, narrower posteriorly than anteriorly 

 (figs. 10, 11, and 12); tail usually shorter than hind foot (in Synaptomys 

 slightly longer) ; palms and soles usually without distinct tubercles. 



MicroH. — Skull comparatively slender and lightly built; lower 

 incisors long, with roots ending on outer side of molars (PL III, figs. 2 

 and 3); crowns of maxillarj^ teeth distinctly narrower posteriorly than 

 anteriorly (figs. 17, 19, 21-35); tail usuallj^ much longer than hind foot 

 (in the Asiatic si:>ecies of Lagurus distinctly shorter) ; palms and soles 

 always with distinct tubercles. 



In external appearance the lemmings and voles differ considerably. 

 The former are mostly thick-set animals, with powerful fossorial feet, 

 long, dense fur and very short tails, while the latter are more slender, 

 with longer tails and with the fur and feet not so highly modified. 



^ = Arvicolin(v Aiict. This name, however, must be abandoned, together with the 

 generic name Arvicola (see p. 14). 



= S'njlineinw Auct. As Siphneus (Brants, 1827) must give place to Myotalpa (Kerr, 

 1792) (see Allen, Bull. Am. Mus. Nat. Hist., New York, YII, p„ 183, 1895) it is neces- 

 sary to makp a corresponding change in the name of the subfamily. 



^The characters separating the Myotaljnnw from the Microtincv are of much less im- 

 portance than those separating the latter from any of its other allies. So close, indeed, 

 is the resemblance between the two that it may eventually prove necessary to unite 

 them under one name. Lack of material jjrevents any final conclusion at present. 



