﻿20 



NORTH AMERICAN FAUNA. 



[No. 12. 



strictly terrestial. This proved unsatisfactory because the two were 

 found to intergrade imperceptibly. Hence be proposed to rearrange 

 tbe species according to the length of the ears. The first division, or 

 that in which the ears are extremely short or apparently absent, he 

 named Hemiotomys, This the author subdivided into two sections, 

 neither of which, he named. The first contained one species, Arvicola 

 fidi'us (=Microtus arvalis), distinguished by its short tail and by the 

 supposed absence of external ears. The second contained the water 

 rat. To Arvicola {=2Iicrotus) proper were referred the three species, 

 arraJiSj suhterraneuSj and rufescens {=Uvofomys gJareoJus). Six years 

 later, in his Etudes cle Micromammalogie, De Selys Longchamps fol- 

 lowed the same system of classification, but considerably extended it 

 and included species from Asia and i^'orth America. This later scheme 

 is as follows: 



The genus is first divided into two sections, one of which consists of 

 si)ecies with ears shorter than the fur and with yery small eyes, the 

 other of species with the ears as long as the fur and with the eyes Avell 

 developed. The first section contains two groups, (1) Hemiotomys with 

 the Euroi)ean water rats and the American ArvicoJa riparius {=Microtns 

 2)e)msylvanicus)j and (2) Microtus with the species/w/r^^s, sai- 'u^ oeconomus^ 

 and certain American forms not mentioned by name. The second sec- 

 tion is divided into three groups: (1) Arvicola with the species subter- 

 ranens, arvalis, gregalis, alUarius, duodecimcostatus^ and socialis; (2) 

 Jfyodes with the two species ruhidus [=Evotomys glareolus) and rutilus 

 [=Evotomys rutilus) ; (3) Mynomes with the s^ieGies rat ens is {=2Iicrotus 

 jjennsylvanicus). These groups and sections the author considers in no 

 way entitled to rank as genera or subgenera. He names them merely 

 for convenience.^ In a postscrii)t published at the time of distribution 

 of the last copies of the Essai Monographique, twenty-six years after 

 its appearance, the author makes a few corrections in the classification 

 Ijreviously adopted. He points out that his Arvicola fulvus is merely 

 a young specimen of A. arvalis that by accident had lost its external 

 ears, and, furthermore, that the si)ecies suhterraneus should be trans- 

 ferred to the section Microtus. 



The classification as finally perfected is as follows: 



Genus Arvicola: 



Group Hemiotomys (water rats). 

 Group Microtus {suhterraneus and savii). 

 Group ArvicoJa (typical voles). 

 Group Myodes (glareolus). 

 Group Mynomes (jyennsylvanicus). 



1 Je dois prerenir que je m'opposerais entierenieut a Televation d'aucune de ces 

 sections au rang de genre ou de sous-genre. Toutes passent de Pune a I'autre par| 

 des nuances insensibles dans la longueur de la queue et des oreilles: et, quant auJ 

 caractere tire de la racine des dents, il est probable qu'il existe a uu degr6 plus oul 

 moins fort chez d'autres especes. Si je me suis permis d'imposer a ces groupes deal 

 noms latins pris parnii les synonymes du genre, ce n'est nullement pour qu'ils puissenia 

 etre introduits dans la nomenclature binaire, mais pour donner aux strangers Tid^el 

 des divers noms que j"ai employes en frau^ais. (Micromammalogie, p. 87.) I 



