322 Mr. Oldfield Thomas on a neio Species of 



which are narrow, especially the latter, and defined by dis- 

 tinct margins. Colour light brown, covered with a very thin 

 epidermis. Interior whitish, inclining to a pinkish tint to- 

 wards the umbones ; and the extreme outer edge is pinkish 

 red and smooth. Hinge composed of a single tooth in the 

 right valve, and two diverging ones in the left. Lateral teeth 

 in right valve consisting of a thin marginal raised acute 

 ridge extending nearly as far as the anterior dorsal slope. A 

 similar ridge is met with in the left valve, only on the posterior 

 dorsal margin. In each valve on the opposite side to the ridge 

 is a narrow groove for the reception of the ridge in the oppo- 

 sing valve. Muscular scars small, posterior one the narrower. 

 Diam. 15 millims., length 12i, thickness 6. 



Hah. 52° 45' S. lat, 50° 39' W. long., 48 fms. East of 

 Uruguay. 



This species is remarkable on account of the squareness of 

 its form, especially at the anterior extremity. 



XL. — Description of a new Species of AxviccAa, from Northern 

 India. By Oldfield Thomas, E.Z.S., British Museum. 



Among the collections received by the British Museum from 

 the India Museum at South Kensington was a specimen 

 labelled and entered in the catalogue as Cricetus songarus 

 (Pall.) *. When the skull was extracted, however, it proved 

 to be, not a Cricetus, but an Arvicola, quite distinct from any 

 species yet described. It was collected in Kumaon by Capt. 

 (now Lieut.-Gen.) R. Strachey, after whom I propose to name 

 the species 



Arvicola Stracheyi, sp. n. 



General colour of the fur above pale brownish grey, the 

 hairs being of a slaty blue colour for three fourths of their 

 length and their ends being brownish yellow tipped with 

 black. On the belly the light tips are replaced by pure 

 white. Ears rather short, scarcely showing beyond the fur, 

 and thickly clothed with hair coloured like that on the back. 

 Feet and tail pure white, the latter with a terminal pencil of 

 hairs nearly half an inch long. Thumbs quite rudimentary. 



The dentition of this species is very interesting, as the third 

 upper molar is of a most remarkable type, and one apparently 

 peculiar to the Arvicolas of this region, the only other species 

 at all resembling A. Stracheyi in this respect being A. Sto- 

 liczlcana, Blanf.f, from Yarkand and Ladak; but even in that 

 the peculiarity is not so strongly marked. 



* Horsfield, Cat. Mamni. Mus. E.I. Comp. p. 145 (18-51). 

 t W. Blanl'ord, J. A. S. B. 1875, pt. ii. p. 147 ; Mamm. Yark. Exped. 

 p. 43, pi. viii. %. 1 (animal), pi. x. B. fig. 2 (skull and teeth). 



