304 MICROTIN^ 



from five inner and five outer to three outer and two inner angles. 

 In all species the first outer infold of m^ is shallow, so that the 

 anterior loop and the first or small external triangle behind it 

 are more or less widely confluent with each other. In this 

 respect Alticola agrees with many of the species of Eothenomys, 

 Anteliomys, Hyperacrius and some other genera. 



Subgenera. — Two subgenera are now recognized, namely, 

 Alticola, comprising the great majority of the species, character- 

 ized by its normal skull ; and Platycranius, comprising one or 

 two species with remarkably depressed skulls. 



Subgenus : Alticola Blanford. 

 (Synonymy under the genus above.) 



Range and characters as described under the genus. 



Interrelationships of the species. — By searching the known 

 forms for the most primitive expressions of each character subject 

 to variation in the genus, it is possible to arrive at a sum which 

 must express the highest degree of specialization possible for the 

 common ancestor of the living members of the genus. In that 

 ancestor the fur was probably short and overtopped by the 

 moderately large ears ; the colour must have been at least as dark 

 as in A. roylei roylei, dark brown above with the lower surface 

 dingy and not contrasted ; the hands, feet, and tail must have 

 been dusky above. In the hands and feet the claws were short 

 and not covered by long hairs growing upon the dorsal surfaces 

 of the digits ; the vestigial thumb bore a small nail or claw ; the 

 palms and soles were not very densely haired behind the pads, 

 and the spaces between the pads were naked. The tail, as in 

 A. argurus, must have been longer than half the length of the head 

 and body, very imperfectly clothed, its short hairs not concealing 

 the scaly annulations and scarcely forming a terminal pencil 

 (cf. A. r. roylei). As in all known species the under surface of 

 the tail is whitish, in the ancestor the tail was probably already 

 bicoloured. Other ancestral characters, common to all the species 

 of the genus, are the possession of five palmar and six plantar 

 tubercles and the mammary formula 2 — 2 = 8. 



The skull was probably lightly and delicately built, much as in 

 A. blanfordi, with the temporal ridges widely separated throughout, 

 and the auditory bullae and the cheek-teeth of moderate size. The 

 enamel pattern of m^ and m-^ must have been as complex as in 

 A. phasma; but the other cheek-teeth had already acquired the 

 reduced form which characterizes them in most of the higher voles. 



The living species of Alticola are all very closely related to each 

 other. Although they vary considerably in external appearance, 

 they are all much alike in skull and dentition. Their skulls differ 

 only in small details correlated with slight differences in the develop- 

 ment of the anterior portions of the temporal muscles, in the size 



