﻿July, 1896.] 



SUBGENUS LAGURUS. 



51 



teeth a drawii-otit appearance, wliich is highly characteristic. Wide 

 reentrant angles occur in the teeth of the young of all Microti; in 

 Lagiirus this embryonic character is retained by the adults. 



Front lower molar. — The number of loops and triangles in the first 

 mandibular tooth is the same as in true Mkrotus. In Microtns prze- 

 icalsMi and Microtns luteus the anterior loop is simple and much 

 reduced, while in Microtns lagiirus and M. palUdus the loop is exactly 

 as in Microtns arvalis. 



Bacli upper molar.— The posterior maxillary tooth differs considerably 

 in form among the various species. In certain American species the 

 loops and angles are arranged exactly as in M. (Arvicola) terrestris, 

 while in M. przewalsl^ii and M. luteus the tooth, although retaining the 

 same number of elements, is remarkably like that of some of the spe- 

 cies of Alticola. (See PL XIII, Wissensch. Eesultate der von X. 

 M. Przewalski nach Cent.-Asien untern. Eeisen. ZooL Theil, Bd. T, 

 Lief. 3.) This resemblance to Alticola results from the unusual elonga 

 tion of the i^osterior loop. In Microtns lagnrus there are three tightly 

 closed triangles, and the terminal loop has a well developed salient 

 angle on each side at the base. 



Otlier teeth. — In the Old World species (fig. 25) the back lower molar 

 contains four tightly closed triangles. The American species, however 

 (fig. 25), so far as known, have only three closed triangles in this tooth. 

 The other molars are always formed as in tetramerodont 2Iicrotus. 

 There is nothing peculiar about the incisors. 



Mammcc. — In Microtns pallidns, or a closeh" related form, there are 

 eight mamm?e, four pectoral and four inguinal. I have been able to 

 find no statement of the number of mammne in the Asiatic species. 



Feet. — Soles densely hairy as in PJiaiomys and the lemmings; plantar 

 tubercles, five ; claws moderately developed, those on hind feet longest. 



Far. — The fur is full and soft, but not highly modified. In color 

 most of the species are dull yellowish or grayish. The marking of 

 Microtns lagurns is unique in the genus Microtns on account of the 

 strongly developed and sharply defined dark dorsal streak. 



Ge7ieral remarls, — The subgenus Lagurns is a strongly characterized 

 group, but, as Dr. Merriam has remarked,^ the species show no pecul- 

 iarities to separate them generically from Microtns arvalis. In Microtus 

 lagurns, M. luteus, and M. pr.zeicalslii, the tail is usually shorter than 

 the hind foot, thus adding to the superficial resemblance to the lem- 

 mings, other voles have the tail so short. 



The subgenus Lagurns is represented in the Old World by 2Iicrotus 

 lagnrus (Pallas), M. luteus (Eversmann), and M. przeicalsldi (Biichner). 

 In America there are probably numerous species and subspecies. 

 Among these may be mentioned Microtus pauperrimns (Cooper), 21. 

 curtatus (Oope), and M. palUdus (Merriam). 



^ American Naturalistj XXIX, p. 758, August, 1895. 



