MURID^— ARVICOLIN^— MYODES. 237 



Genus MYODES, Pallas. 



Mus sp., Linn^us, and other earliest writers. 

 Arvicola sp., of different writers. 

 <^Hypudmus, Illiger, 1811, in part; includes Mus lemmas, ampliibius, &c. ; not of late writers. 

 <^Lemmus, Linck (fide Baird), in part ; includes the Armcolce. 

 ^Georychus, Richakdson, F. B.-A. i, 1829; and Aud. & Bach., Q. N. A. iii, 1854, in part ; includes Cunicu- 



lus; not of Illiger, which belongs to an entirely different family. 

 <^Myodes, Pai.las, Zoog. R.-A. i, 1831, 172, in part ; iucludes Arvicola, and thus about equal to his "Mures 



cunicularii" of 1778. 

 = Myodes, Coues, Proc. Acad. Nat. Sci. Phila. 1874, 194. 



Cranial chars. — 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; bullse 

 ossese 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 fossae that occur in most Arvicolince 

 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. 



Dental 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 Arvicolince, 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 reentrances very deep, 

 reaching almost across the teeth, the external saliencies very acute ; of the 

 under series, the internal reentrances very deep, reaching almost across the 



