MURIDA—ARVICOLIN AI—ARVICOLA. 149 
produces a tooth that Zooks radically different in sculpture. The front lower 
molar carries the same general plan of oppositeness 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 admost 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, Lacépéde. 
< Mus, Linn.xus, Syst. Nat. i, 1766, and most early authors. 
< Mures cunicularii, PaLuas, N. Sp. Glirium, 1778, 77. 
<Lemmus, Linck; Fiscuenr, et al. 
Myodes, PALLAS, Zoog. R.-A. i, 1811, 172. Not Myodes of Selys-Longchamps, 1839, which = Hypudaus, 
Keyserling and Blasius. 
<“Arvicola, LackrEpE, Tableau, 1803” (fide Agassiz), and most late authors. Includes amphibius and 
arvalis. 
<Hypudeus, WwuicEr, Prod. 1811. Not of Keyserling and Blasius, nor of Baird. Includes Mus lemmus, 
amphibius, and arvalis. 
> Mynomes, RarrNEsQue, Am. Monthly Mag. ii, 1817, 45. Type, M. pratensis = Wilson’s Meadow-mouse, 
= Arvicola pennsylvanica Ord. 
> Psammomys, LEContrE, Aun. Lye. Nat. Hist. N. Y. 1829, 132 (pinetorum). Not of Rueppel. 
> Pitymys, McMurtrir, Am. ed. Cuy. R. A. i, 1331, 434. Type, 4. pinetorum, LeC. 
> Hemiotomys, SELYS-LONGCHAMPS, Etudes de Microm. 1839 85 (includes amphibius, terrestris, &c.). 
> Microtus, SELYS-LONGCHAMPS, op. cit. 1839, 85. 
> Pinemys, Lesson, Nouv. Tab. R. A. 1842, 12 ( pinetorum). 
> Hemiotomys, Barrp, M. N. A. 1857, 515. Type, Arvicola riparius Ord. 
> Pedomys, Bard, op. cit. 517. Type, Arvicola austerus LeC, 
> Chilotus, BarrD, op. cit. 516. Type, Arvicola oregoni Bach. 
The foregoing synonymical list of itself indicates the limits we wish to set 
to Arvicola. All the earlier names, Mus, Lemncus, Myodes, Arvicola Lacép., 
and Hypudaus Ml, marked <, were of wider applicability than Arvicola, as 
we define it, is; for they all (unless Arvicola Lacép. be an exception) 
included the Lemmings, and made no distinction of the rooted-molar species 
of what Keyserling and Blasius afterward called Hypudeus, 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 
