MURIDH—ARVICOLINA—MYODES. 239 
each other, the 1st much shorter, the 5th shorter still; soles usually densely 
furry to the claws, but sometimes showing the under surface of the toes; 
plantar tubercles naked. Tail very short, its vertebrae shorter or not longer 
than the sole, leporine, stout, densely hairy throughout, with a copious ter- 
minal pencil, often longer than the vertebre. 
The foregoing diagnosis, so drawn as to exclude Cuniculus, is based upon 
Mus lemmus of Linnzeus, and indicates a perfectly natural generic group of 
Arvicoline. From Arvicola, in any of its subgeneric phases, Myodes is prom- 
inently distinguished by external form as well as by cranial and dental char- 
acters. The general clumsy shape, very convex-obtuse head, short rabbit-like 
tail, short ears, small furry feet, elongated fossorial claws, and mollipilose 
pelage, are associated, in the skull, with breadth and massiveness, laminar 
expansion of the zygomata, and a peculiar shape of the palate ; and, in the 
teeth, with stoppage of the root of the under incisor opposite the last 
molar, a quill-like beveling of the upper incisors, and a particular pattern of 
the molar crowns. All the points of external form that mark off M/yodes from 
Arvicola likewise separate it from Synaptomys ; these two agreeing almost 
precisely in cranial and dental characters. The plane, instead of grooved, 
upper incisors are distinctive of Myodes, and so is, to less degree, a slight 
difference in the middle lower molar (wide descriptions). With Myodes, 
Cuniculus is generally associated generically ; but we wish to particularly 
signalize the fact that they are perfectly distinct genera. Although both of 
them are ‘‘lemmings”, so called; and although they do agree in general 
external tournure, yet they present differences fully on a par with those made 
the basis of generic distinctions in other cases. How great these differences 
are may be inferred, by one not acquainted with the animals, from the fact that 
Lilljeborg, who adopts only four genera for the whole subfamily, keeps the 
two apart, his genera being Fiber, Arvicola, Cuniculus, and Myodes. he 
comparative diagnoses are fully given farther on; here we will only add, that 
in Myodes the external ears, though small, are perfect, while Cuniculus has 
no external ears; that in Myodes, though the fore claws are lengthened and 
“fossorial”, they never show the extraordinary development seen in Cuniculus; 
that the rudimentary pollex of Myodes bears a large ligulate nail, only faintly 
indicated in Cuniculus by an abortive thumb and claw; and, finally, that with 
most cranial characters in common, the pattern of the molars is very different 
in the two genera. Unlike Myodes, Cuniculus turns white in winter. 
