MURID^— AEVICOLINJE— CHILOTUS. 207 



Subgenus CHILOTUS, Baird. 



Arvicola sp., Auctorum. 



= Chilotus, Baird, M. N. A. 1857, 516 (typo, A. orcgoni Bach.).— Codes, Proc. Acad. Nat. Sci. Pbila. 1874, 190. 



Chars. — Very small. Pelage and proportions of parts as in Myonomes, 

 but the ears "small, orbicular, the marginal portion or helix incurved all 

 round, bounding a distinct fossa innominata; the upper and lower roots so 

 close together as to be confluent externally, and thus enclosing the meatus 

 entirely in the anterior rim, however low. Surfaces of the ear almost naked"; 

 plantar tubercles only 5 (?). Dentition combining the anterior lower molar 

 as in Myonomes, with the middle and back upper molars as in Pedomys "or 

 Pltymys (other teeth as in Arvicola generally, and therefore not diagnostic). 



Further details of this section are given under head of its type and only 

 known species. 



ARVICOLA (CHILOTUS) OREGONUS, Bachman. 



Oregon Meadow Mouse. 



Arvicola orcgoni, Bachman, Journ. Acad. Nat. Sci. Phila. viii, 1839, CO ; Townsend's Narrative, 1839, 315. — 



Aud. & Bach., Q. N. A. iii, 1853, 232, pi. clxvii, f. 3. 

 Arvicola {Chilotus) orcgoni, Baird, M. N. A. 1857, 537. 

 Arvicola (Ckilotus) oregonus, Codes, Proc. Acad. Nat. Sci. Phila. 1874, 190. 



Diagnosis. — Arvicola minimus (S-o^-jm/L), palmis dimidium plantarmn 

 (s : §); caudd capitc longiore (I4); auriculis cxiguis, occult is, subnudis, mar- 

 gins plicata. Color ibus fere ut in A. ripario. 



Least Meadow Mouse, with the colors much as in A. riparius, the ears 

 small, hidden, nearly naked, with folded margin and the meatus rimmed about ; 

 3-3J inches long, tail 1\, or with the hairs 1J, thus longer than the head, and 

 nearly twice as long as the soles, these twice as long as the palms. 



(No. tMI) At first sight, this little animal looks like a half-grown 

 riparius ; the next glance, however, shows that it is perfectly adult, and 

 further examination reveals the peculiarities given in the foregoing diagnosis 

 and in the notice of the subgenus. The fur lias exactly the texture of that 

 of riparius, and the coloration is much the same as in typical examples of 

 the latter — a grizzle of yellowish-brown, rufous-gray, and black, darkest along 

 the middle line of the back; beneath dark plumbeous, strongly hoary; tail 

 indistinctly bicolor, to correspond. In fact, the external characters, both of 

 color and proportions, are so much like those of riparius, with one exception, 



