134 MR. O. THOMAS ON A N KW GENUS OF MURID^. [Feb. 21, 



with tlie Old- World I-Iam.slers under the naii:e of Cricctus, the latter 

 group, however, forming itself a subgenus, equal in rank to those 

 now commonly admitted among the American Vesper-Mice. 



This change, large as it is, will be rendered rather less unaccept- 

 able by the consideration that the name Hesperomys ' has itself, by 

 the strict laws of nomenclature, no possible claim to adoption, being 

 antedated not only by Calomys ", Waterh., and the other earlier names 

 of the same author, and by EiUjmodontia, F. Cuv. '\ but also by 

 Akodon, Mcyen ', founded on a now almost unrecognizaMe specimen 

 belonging to Waterhouse'h subgenus " Ilabrothrix." That this name 

 vfould have been brought up and forced into use may be looked upon 

 as certain, and in fact the first step in this direction has been taken 

 by the substitution of Akodon for Habrothrix in Trouessari's list of 

 Rodents '\ From the point of view ot nomenclature, therefore, the 

 junction of Cricctus and Hesperomys is not so wholly a misfortune 

 as it otherwise might have been. 



As to changes in specific names, it fortunately happens that those 

 used in the two genera have for tiie most part been different, the 

 two species mentioned in the subjoined footnote "^ representing ap- 

 parently all the necessary alterations. 



Then as to the geograi)hical distril)ution of the two forms, nothing 

 is more natural than that a genus ranging all over America, from 

 British Columbia to Cape Horn, should also be found, like the majority 

 of the mo-t typical North-American genera, in Siberia, China, and 

 the Eastern Palsearctic Region generally. 



With regard to the opinions of other authors on the relations of 

 Cricctus to Hesperomys, it is interesting to find that in Dr. Winge's, 

 recent careful and elaborate work ^ on the Rodents of Lagoa Santa, 

 Brazil (a work in which the whole interrelations of the Rodents are 

 freshly considered and described), the differences between Cricctus 

 and Hesperomys are shown to be almost nil '*, and that in the Synopsis 

 of the Muridse he has had to separate the genera merely into those 

 from the Old World and those from the New ". He does not, how- 

 ever, notice the necessity for actually uniting Cricctus with Hes- 

 peromys, no doubt because of the very different standard of generic 

 rank he adopts. Thus he recognizes the well-known Subgenera 

 Habrothrix, (Dxymyctcrus, Scapteromys, Calomys, and Rhipidomys 

 all as full genera, and therefore naturally admits Cricetus also. I 



1 Zool. Voy. ' Beagle,' Mamm. p. 75 (1839). 



2 P. Z. S. 1837, p. 21. 



■* Aun. Sci. Nat. vi. p. 168 (1837). 



<! N. Act. Ac. Leop. xvi. p. (iOO (18S3\ 



^ Bull. Soc. Sci. Auvers, 1880, p. 140. 



^ Cricctus ohsciirus, M.-Eclw., nee HiS^icromys ohscurus, Waterh., ir.ay stand 

 as C. viongolicus. 



Cricetus lonyicaudatus, M.-Edvr., nee Hesperomys lungicavdaiiis, Ecui;., ;is C. 

 chinensis. 



Cricctus cinerciis, Gerrard, Cat. Bones Maunn. B.M. p. 172 (1862), appears 

 never to have been described, and does not therefore invalidate the -specific 

 name of my Cricetus {77/omaso7?i//s) cinercus, P. Z. S. 1882, p. 108. 



^ E Musco Lundii, vol. iii. 1887. 



^ L.c. p. 11. " L.c. p. 12'.. 



