i!« 



f! 



I, ' 



m ' 



150 



MONoouArns op north American rodentia. 



vaiimis sections iil' \\w i;(Miiis llmt it is quite wortii while to recognize. The 

 niinics l'.i(i)iimomijs LrC. {iwc Rupp.), PUymys McMurt., and I'incmys Less, 

 are mere synonyms, nil having been based on the same annual (pinetorum), 

 and two of them being simply amends for LcCoiite's mistake in taking 

 I'tiiimmoinyi Riip|». for his Ani'wola pinetorum. *^ Mlcrotus" Solys. appears 

 to bo about the same tiling as PUymys. Ilem'wtomys Selys. {nee Baird) goes 

 to the VA\ro\')cm\ amphibius. Myonomes Raf and Pcdomys and Chilotus Baird 

 are tcnaljle sul)gonerio names for particular American groups. Doubtless 

 there are some other generic or subgencric names that have not como to our 

 notice. 



In proceeding now to define Arvicola, we may premise that our dias;- 

 nosis of the genus will simply be equivalent to such restriction of the char- 

 acters of the subfamily Arcicollnce as will exclude tiie Lemmings, the 

 remarkal)l<^ Synnjifomys of Haird, and tiic rooted-molar group {Ei'otomys nob. 

 := Ilyjiiiilceus Keys. Bias. Bd. nee 111.). Some of the more boreal Arvicola do 

 indeed closely approximate to the Lemmings in the shortness of their ears, tail, 

 and feet, and in the mollipilose pelage; but the radical differences in dentition 

 arc never, so far as wc know, obscured. It may be that there are some 

 species of Arvicolincc that require generic separation from Arvicola besides 

 tiiose just mentioned, but none such have come to our knowledge. 



Some of the characters we arc al)out to give are rather those of the sub- 

 family than of the genus; but the particular combination, as expressed in the 

 whole paragraph, is generally diagnostic. • ' ' • ' , ',' ; 



Gkn. Chars. — Ciownsof the (^, rootless, perennial, prismatic) molars 

 plane, divided into several closed islands of dentine by folds of the surround- 

 ing sheet of enamel that meet from opposite sides and fuse along the median 

 line (cf Erotomyn) ; the saliencies and reontrances of the alternating prisms 

 strong and sharp, equally so on both inner and outer sides of the molar series, 

 the profile of which is therefore equally serrate on both sides (cf Myorlet, 

 Synnptotny."). Anterior upper molar of 5 prisms, — 1 anterior, 2 interior, 2 

 exterior. Middle upper molar of 4 (or 5) prisms, — 1 anterior, 1 interior, 2 

 exterior (the last sometimes giving off a supplementary postero-intcrior one). 

 I'osterior upper molar of 4 to 7 prisms, of which the first is always anterior 

 and transverse, the last a variable treffle (C, G, U, V, Y, &c., in siiape, 

 according to subgenus or species), and the intermediate ones lateral and alter- 

 nating. All upper molars subcquul in length and breadlii (cf. Myodas, Synap- 



