MURIDJE— ARVICOLIjNLE— ARVICOLA RIPARIUS. 157 



Arvicola albomfeseens, Emmons, Eep. Quad. Mass. 1S40, 00 (Massachusetts; partial albino). — DeKay, N. 



Y. Zool. i, 1842, 89 (same as Emmons's). 

 Arvicola hirsutus, Emmons, Rep. Quad. Mass. 1840, 60. — DeKay, N. V. Fn. i, 1842, 86 (same as Emmons's). 

 Arvicola nasnla, Bachman, Journ. Acad. Nat. Sci. Plnla. viii, pt.ii, 1842, 396 ( Massachusetts). — Aud. & Bach., 



Q. N. A. iii, 1853, 211, pi. clxiv, f. '2 (Massachusetts, New York, ami Michigan ). — LeConte, 



Proc. Acad. Nat. Sci. Phila. vi, 1853, 407 (quotes "Wiegmann's Archiv, 1843, 52, and Schiuz, 



251"). 

 Arvkola oneida, DeKay, N. Y. Zool. i, 1842, 88, pi. xxiv, f. 1 (young; New York).— LeConte, Proc. Acad. 



Nat. Sci. Phila. viii, 1853, 400 (same as DeKay's). 

 Arvicola rufescens, DeKay, N. Y. Zool. i, 1842, 85, pi. xxii, f. 1 (Northern New York). 

 Arvicola occicleiitalis, Peai.e, Mamm. U. S. Expl. Exped. 1848, 45 (Puget.'s Sound). — LeConte, Proc. Acad. 



Nat. Sci. Phila. vi, 1853, 408 (same as Peale's).— Aud. & Bach., Q. N. A. iii, 1854, 294 (same 



as Peale's).— Baird, M. N. A. 1857, 534 (Peale's type described). 

 Arvicola californica, Peale, Mamm. U. S. Expl. Exped. 1848, 40 (California).— LeConte, Proc. Acad. Nat. 



Sci. Phila. vi, 1853, 408 (same as Peale's).— Aud. & Bach., Q. N. A. iii, 1854, 293 (same as 



Peale's).— Baird, M. N. A. 1857, 532 (Peale's type). 

 Arvicola montana, Peale, Mamm. U. S. Expl. Exped. 1848, 44 (Mount Shasta, Cal.). — Add. & Bach., Q. 



N. A. iii, 1854, 302 (same as Peale's).— Baird, M. N. A. 1857, 528 (California and ? Nebraska).— 



Newberry, P. R. R. Rep. vi, 1857, Zool. 61. 

 Arvicola edax, LeConte, Proc. Acad. Nat. Sci. Phila. vi, 1853, 405 (California).— Aud. & Bach., Q. N. A. 



1854, iii, 270, pi. 154, f. 2 (taken from LeConte's type, and description compiled from 



LeConte). — Baird, M. N. A. 1857, 531 (description from LeConte's type). 

 Arvicola uorealis, LeConte, Proc. Acad. Nat. Sci. Phila. vi, 1853, 407, excl. synon. (not of Richardson, &c. 



The species is based upon specimens from Rhode Islaud now in Mus. Smiths.). 

 Arvicola trotebridgei, Baird, M. N. A. 1857, 529, in text (name suggested from some supposed dental pecul- 

 iarities of No. yWVi Mus. Smiths., from Monterey, Cal.). 

 Arvicola longivostris, Baird, M. N. A. 1857, 530 (based on supposed cranial peculiarities of No. Jff§, Mus. 



Smiths., from California). — Newberry, P. R. R. Rep. vi, 1857, Zool. 01. 

 Arvicola modcsta, Baird, M. N. A. 1857, 535 (based on No. tV'/V, from Rocky Mountains; very young). 

 Arvicola rvfidorsum, Baird, M. N. A. 1857, 520 (Holmes' Hole, Mass. ; a very red specimen). 

 Arvicola breiceri, Baird, M. N. A. 1857, 525 (bleached breed from Muskeget Islaud, Mass.). 



Skull. — The cranium of Arvkola riparius has not a single specifically 

 diagnostic feature ; all its characters are subgeneric, shared by xanthognatliu?, 

 and by the various geographical strains more or less deviating in external char- 

 acters from ordinary riparius of the United States. It averages, of course, 

 smaller than that of xanthognathus or even of var. townsendi ; but the mini- 

 mum of both of these is within the average of riparius. Our table of meas- 

 urements indicates both size and shape so perfectly that these points need not 

 detain us here. The skull is not satisfactorily distinguishable, dentition aside, 

 from that of Pedomys; for the difference in the length of the nasal branches 

 of the intermaxillarics, given by Baird, does not always hold. From Pitymys, 

 it may generally be known (dentition aside) by being larger and not quite so 

 wide for its length (as 0.59 to 1.00, instead of 0.62 to 1.00, as in Pitymys). 

 It averages much larger than that of Cli'dotus oregoni. 



The dentition, likewise, offers nothing specifically diagnostic; all the 

 species and varieties of the subgenus having the same pattern of the molar 

 crowns. The present opportunity, however, is taken to fully describe the 



