﻿66 



NORTH AMERICAN FAUNA. 



[Ko. 12. 



inaudibular tooth, ArvicoJa by tlie presence of large musk glands on 

 the sides, Fedomi/s and Fiiymys by reduction in the numbers of both 

 mamma* and plantar tubercles. Cliilotus by reduction in the latter onlj^, 

 and Fhaiomijs by an increase in the number of mamma^ and by the 

 very large claws. More extended comparisons will be found under 

 each of these subgenera. 



This subgenus is the most widely and generally distributed, as well 

 as the one containing the largest number of species. Although the 

 species of ^Iic7^otincv are still very imperfectly known, there is little 

 doubt that the members of the subgenus Microtus greatly outnumber 

 the species of all the other genera and subgenera together. Conspicu- 

 ous representatives of the subgenus Microtus are (in the Old TTorld): 

 Mlcroins arvaJis (Pall.), M. agrestis (Pall.), J/, ratiiceps (Keys. & Bias.), 

 M. nivalU (Martins), 21. (juentJien (Dansford cS: Alston), M. silcMmensis 

 (Hodgson)^ (in America): Microtus pennsyJvanlcus (Ord), M. terrccnovce 

 (Bangs), M. xantlwgnatlius (Leach). M. clirotorrMnus (Miller), M, longi- 

 catida (Merriam), M. mogoUonensis (Mearns), M. toicnsendi (Bachman). 



Subgenus AR VIC OLA Lacepede. 



1801. Arvicola Lacepede, Mem. de I'Institut, Paris, III. p. 489, 1801 (genus). Type, 



'Arvicola ain2)]iil)ius' — Itus terrestris Liuu. 

 1883. Arvicola Lataste, Le Xatnraliste, Tome. II, p. 349, 1883 (subgenus). 

 1836. JSemiotomys De Selys Longcbamps, Essai Mouograpbique sur les Campagnols 



des environs de Liege, p. 7, 1836, part (included arvalis and terrestris). 

 1857. PaludicoJa Blasius, Fauna der Wirbeltbiere Deutscblauds, I, p. 333, 1857, part 



(included terrestris, nivalis, and ratticeps). 

 1867. Ochetomys Fitzinger, Sitzungsber. K. Akad. AViss. Wien, LYI, -p. 47, 1867. (N,o 



type mentioned^ but genus intended to include all tbe water rats of Europe.) 

 1867. FraticoJa Fatio, Les Campagnols du Bassin du Leman, p. 36, 1867, part (included 



terrestris, nivalis, arvaJis, ratticeps, and campestris) . 

 1894. AuJacomys Rboads, American Naturalist, XXVIII, p. 182, 1894. Type, Aulacomys 



arvicoloides Rboads. 



Geogra2)hic distribution of type species. — Northern Europe. 

 GeograpMc distribution of subgenus. — Northern part of Northern 

 Hemisphere, exclusive of America east of the Eocky Mountains. 

 Essential characters: 



Palate sligbtly abnormal. 



m 3 occasionally vritb closed triangles. 



m 1 normally with 3 to 5 closed triangles and 7 to 9 salient angles. 



ni 3 normally with 2 or 3 closed triangles and 6 to 8 salient angles. 



Mammte-S. 



Plantar tubercles 5. 



Sole almost naked. 



Claws on bind feet longest. 



Fur sligbtly modified. 



Musk glands present on sides of body. 



SMIL — The skull of the larger Old World species of ArvicoJa (PI. I, 

 fig. 9) is nearly as large as that of Seojiber. In the American species 



