MURID#®—ARVICOLIN 4 —MYODES. 237 
GENUS MYODES, Pallas. 
Mus sp., LINN ZUS, and other earliest writers. 
Arvicola sp., of different writers. 
< Hypudeus, ILLIGER, 1811, in part; includes Mus lemmus, amphibius, &c.; not of late writers. 
<Lemmus, LINCK (fide Baird), in part; includes the Arvicola. 
<Georychus, RICHARDSON, F. B.-A. i, 1829; and Aup. & Bacu., Q. N. A. iii, 1854, in part; includes Cunicu- 
lus; not of Iliger, which belongs to an entirely different family. 
<Myodes, Pauas, Zoog. R.-A. i, 1831, 172, in part; includes Arvicola, and thus about equal to his “ Mures 
cunicularii” of 1778. 
= Myodes, COUES, Proc. Acad. Nat. Sci. Phila. 1874, 194. 
CrantaL cHAars.—Skull massive, low, broad (zygomatic width upward of 
two-thirds the length) ; cranial portion encroaching upon the orbital cavities 
with a strong salience; rostral portion obtuse, broad, short (about one-fourth 
the entire length), not narrower than the interorbital constriction; nasals and 
intermaxillaries subequal in length, falling short of the orbits; anteorbital 
foramen small, nearly underneath the anterior root of the zygoma; malar 
branch of maxillary, and jugal itself, expanded into a broad lamina; bulle 
osseze moderate, their inner borders approximated and nearly parallel through 
narrowness of basioccipital ; incisive foramina short and narrow, not reaching 
to opposite anterior molars; palate ending behind as an emarginated shelf 
(with or without a median azygos projection) opposite the interspace between 
the penultimate and last molars, and the space between these teeth of opposite 
sides thus broadly open, but the lateral fossee that occur in most Arvicoline 
still evident, though pushed forward under the edge of the palatal shelf; ptery- 
goid processes widely divergent and very low; under edge of lower jaw very 
broad from passage along it of root of incisor; ramus of lower jaw thin and 
plane, from lack of incisor-root extending up it; descending process strong, 
flattened underneath, and much twisted ; apex of coronoid as high as condyle. 
Denrat cHars.—Molar series long (more than one-fourth the length of 
the skull), strongly convergent anteriorly, and the individual teeth large. 
Molars strictly of the prismatic type characterizing Arvicoline, but in the 
details of their crowns different from those of any genus except Synaptomys, 
with which they correspond almost precisely; first upper and under molars 
longest, the others successively diminishing a little in length, but all of nearly 
the same width throughout, though the under molar may narrow a little from 
before backward; of the upper series, the external reéntrances very deep, 
reaching almost across the teeth, the external saliencies very acute; of the 
under series, the internal reéntrances very deep, reaching almost across the 
