MUKIDJ3— ARVICOLIN.TC— ARVICOLA. 1 49 



produces a tooth that looks radically different in sculpture. The front lower 

 molar carries the same general plan of opposite ness instead of alternation of 

 the lateral triangles, which, with the distinctly double condition of the 

 indentated angles of enamel, where these meet along the middle, tends to 

 throw, and almost succeeds in throwing, the lateral triangles that occur in 

 Arvicola into larger triangles, reaching quite across the tooth. Thus, from 

 behind forward, there is first one perfect triangular loop reaching across the 

 tooth; next, there are an external and an internal angle opposite each other, 

 inclosing a lozenge that reaches across the tooth; next, there are an internal 

 and an external angle, not quite opposite each other, and therefore forming 

 two nearly separated lateral triangles, generally not completely closed in, 

 however, but more or less continuous with the area of the large anterior 

 trefoil that finishes the tooth in front. 



Genus ARVICOLA, Lacenedc. 



< J/ms, Lixn.eus. Syst. Nat. i, 17(5;'., and most early authors. 

 <Murcs cunicularii, Pallas, N. Sp. Glirium, 1778, 77. 

 <Lemnms, Linck ; Fischer, el al. 

 Myodes, Pallas, Zoog. B.-A. i, 1811, 172. Not Myodts of Selys-Lougebamps, 1839, which = Hypudceus, 



Keyserliug and Biasing. 

 <"Arvieola, Lacepede, Tableau, 1803" (fide Agassiz), and most late authors. Includes amphibius and 



arvalU. 

 <IIypudwits, Illiger, Prod. 1811. Not of Keyserling and Blasius, nor of Baird. Includes Mas lemmus, 



amphibius, and arvalia. 



> Mynomes, Rafixesque, Am. Monthly Mag. ii, 1817. 45. Type, M. pratensis = Wilson's Meadow-mouse, 



= Arvicola pennsylvanica Ord. 

 >Psammomys, LeConte, Ann. Lye. Nat. Hist. N. Y. 1829, 132 (pinetorum). Not of Rueppel. 

 >PUymys, McMurtrie, Am. ed. Cuv. R. A. i, 1831, 434. Type, A. pinetorum, LeC. 



> Hemiotomys, Selys-Longchamps, Etudes de Microm. 1839 85 (includes amphibius, lerreatris, &c). 



> Micro tun, Selys-Longchamps, op. cit. 1839, 86. 



> I'incmijs, Lesson, Nbuv. Tab. R. A. 1842, 12 (pinetorum). 



> Hemiotomys, Baird, M. N. A. 1857, 515. Type, Arvicola riparius Ord. 

 >Pedomys, Baird, op. cit. 517. Type, Arvicola austerus LeC. 

 >Chilotu$. Baird, op. cit. 510. Type, Arvicola oregoni Bach. 



The foregoing synonymical list of itself indicates the limits we wish to set 

 to Arvicola. All the earlier names, Mus, Lemmus, Myodes, Arvicola Lacep., 

 and Hypudceus 111., marked <, were of wider applicability than Arvicola, as 

 we define it, is; for they all (unless Arvicola Lacep. be an exception) 

 included the Lemmings, and made no distinction of the rooted-molar species 

 of what Keyserling and Blasius afterward called Hypudceus, and what we 

 now call Evotomys. The many later names, marked >, are of less enlarged 

 application than our Arvicola, being simply based upon particular species of 

 the genus; most of them will stand as convenient subgeneric terms for the 



