MAMMALIA. 



41 



Proceeding now to the question of nomenclature, it may be as well, before making' 

 any remarks upon it, to quote Mr. Blyth's description I. c. in full. It runs as follows :— 



Phaiomys, nobis, n. g. Similar to Arvicola, but more robust, with a well-developed thumb and nail to the 

 forefoot; tail shortish and densely clad with short adpressed hairs. Tipper rodent tusks inconspicuously grooved. 



Ph. leucurus, nobis, n. s. Length of a female containing six foetus Q\ inch, of which tail \ inch ■} of a 

 smaller specimen sent inches, of which tail 1£ inch, of hind-foot claws (sic, probably a misprint for hind 

 foot with claws) I inch. Pur dense, very soft, and tine; the surface fine greyish -brown on the upper parts; on 

 the lower parts, feet and tail white, a little sullied ; basal two-thirds or more of the upper fur dark slaty. 

 " Ears rounded, of medium size, rather appressed." 



It is, I think, evident from the above, that Mr. Blyth based the distinction between his 

 genus Phaiomys and Arvicola chiefly on the presence in the former of a claw to the rudimentary 

 thumb; neither the general form nor the tail affording any distinctive character of importance. 

 This claw is absent in some species of the genus Arvicola, but present, I think, in a 

 still larger number. It is present, for instance, in the common water rat, A . ampkibius ; Pallas 

 mentions its existence in a more or less rudimentary form in A. socialis," A. (eco)iomus, 3 A. 

 gregalis? A. rutilus, 5 and A. saxatilis, 6 it being very minute in A. gregalis and A rutilus; 

 whilst it is described as absent in A. alliarius. 1 Its presence has, moreover, been noted in 

 some Asiatic forms described in more recent works, as A. amurensis,* A. maximowiczii, 9 

 A. brandti, 10 A. obscurus, 11 and A. mandarinus, 12 and I note, in the first place, that these 

 species belong to very different sections of the genus as distinguished by the characters 

 of the teeth ; A. saxatilis and A. brandti, for instance, having, according to Milne-Edwards, 13 

 one prism on the inner side of the last upper molars, in addition to those found in A . obscurus, 

 A. mandarinus, 1 * and many other species ; secondly, that careful and well-informed observers, 

 with a wide knowledge of the genus, have not considered the presence or absence of a claw on 

 the thumb a character of sufficient importance to justify its being used for generic distinction ; 

 and lastly, that there is an almost complete gradation from species wanting the claw to those 

 which have it well developed, through forms in which it is more or less rudimentary. 



But if Phaiomys leucurus be relegated to the genus Arvicola, the name must be 

 changed, as there is an A. leucurus of Gerbe, 15 described from the Alps of Provence in 



1 Evidently a misprint for ly. Theobald gives as the measurement of the total length 6'15 inches, of which the head was 1'30. 

 and the tail 125. 



2 Glires, p. 220. 



3 lb., p. 234. 

 * lb., p. 244. 



5 lb., p. 248. 



6 lb., p. 256. 



7 lb., p. 253. 



8 Schreuk, Reisen und Forschungen im Amuv-Lande, i, p. 129. 

 ,J lb., p. 140. 



10 Radde, Eeisen im Suden von Ost-Siberien, i, p. 199, PL VII, fig. 3. 



11 Eversman apnd Middendorf , Sib. Reise, p. 109, PI. XI, figs. 1—5. Although the presence of the claw is not mentioned 

 in the description, it is clearly shewn in figure 3 representing the skeleton. The original description of the species, is in the 

 Addenda ad cel. Pallasii Zoographiam, &c, fasc. 2, — a very rare book. 



12 A. Milne-Edwards, Rech. Mam. p. 129, PI. XII, XIII. 



13 Rech. Mam., p. 131. I have unfortunately been unable to consult a paper by Blasius on Arvicola, in the Munch. 

 Gelerht. Anz., 1853, xxxvii, p. 105, as the volume is deficient in the only set in Calcutta, that belonging to the Asiatic Society. 



14 This character, I may note, appears quite as important as the presence of an additional ridge on the anterior upper molars, 

 on the strength of which Hodgson's genus Neodon has been established (Jerdon, Mammals, p. 216). The genus was originally 

 proposed in the Annals and Magazine of Natural History for 1849, Ser. 2, Vol. Ill, p, 203, but it was not described, and 

 it was merely said to differ from Arvicola in the character of the molars. The genus Neodon appears founded on characters of 

 only specific importance, and the type, N. sikkimensis, is, I think, a true Arvicola. 



15 Rev. de Zool., iv, p. 260. 



