INTERRELATIONSHIPS OF GENERA 45 



fossorial life; the fur is short and dense and in one species 

 {H. wynnei) it is highly modified and mole-like ; the eyes and 

 ears are reduced, the fore-claws are slightly lengthened, the tail 

 is shortened, but fully clothed; the mammary formula is 

 reduced to 1 — 2 = 6. The temporal muscles are greatly in- 

 creased in size and strength and the reduction of the eyes is no 

 doubt partly correlated with this muscular increase. In the 

 skull the temporal ridges fuse, at an early age, to form a linear 

 median interorbital crest, and the squamosals, frontals, parietals, 

 and interparietal all show a characteristic temporal modification ; 

 the post-orbital crests of the squamosals are greatly lengthened, 

 extending from the interorbital region outwards and backwards 

 on each side almost to the glenoid articulation. The anterior 

 palatal foramina are reduced to more or less shortened, narrow 

 slits. The palate in the smaller species is essentially as in 

 Alticola ; but in the largest form {H. wynnei) the posterior median 

 sloping septum is represented by a short spine, in form rather 

 like that seen in Anteliomys, but differing in that it is not hori- 

 zontal but sloping ; if this spine were directly connected laterally 

 with the post-palatal pits, the palate in H. wynnei would be 

 similar to that of many species of Microtus ; as it is the pits have 

 already very definite, salient, inner borders, which run forwards 

 to effect a junction with the dorsal surface of each lateral bridge 

 near the base of the spine ; thus the structure of the palate 

 in this species may be said clearly to foreshadow the palate of the 

 higher voles. The presphenoid is reduced to a slender bar in all 

 species of Hyperacrius, and a similar reduction is to be seen in 

 some but not in all species of Alticola. The auditory bullae are as 

 in Alticola as regards essential structure; but they are consider- 

 ably smaller and less inflated. The cheek-teeth are light, rootless 

 and tall-crowned ; they have normally differentiated enamel, 

 but their re-entrant folds lack cement. The enamel pattern is 

 essentially as in Alticola; but m^ is simplified and its posterior 

 end is more reduced and shortened than in any species of 

 Alticola. 



DoLOMYS apparently represents or at least is very nearly related 

 to forms which must have been directly ancestral to the Water 

 Voles (Arvicola). Its fossil remains have been found, hitherto, 

 only in the Upper Pliocene of Hungary; but recently a living 

 species has been discovered on the mountains of Montenegro, 

 where, secure from competition, the genus has survived until the 

 present day. This living species is a large, soft-furred, long- 

 tailed vole, bearing such a close outward resemblance to the Alpine 

 Voles {Microttis (Chionomys) nivalis) that it was at first 

 mistaken for a member of that group. 



As in other primitive voles the cheek-teeth are rooted in 

 adults ; indeed, in this genus the teeth appear to be more 

 brachyodont than is usual in such genera, for even in the living 

 species the cement spaces and pulp cavities close at the bases of 



