338 MiCROTiN-a: 



palatal bridges stout; post-palatal pits deep, their inner borders 

 sharp and salient, each passing forward and curving ventrally to 

 join the dorsal surface of the palatal shelf near the base of the 

 median spine (Fig. 94). 



Cheek-teeth with the structure and enamel pattern (Fig. 956) 

 characteristic of the genus. 



For external and cranial measurements, see tables at end of 

 volume. 



Remarks. — The relationships of this striking species have long 

 been doubtful (cf. Miller, N. Amer. Fauna, No. 12, p. 55, 1896), 

 but a study of the fine material collected at Murree by Mr. H. W. 

 Wells for the Bombay Natural History Society's Mammal Survey, 

 coupled with a re-examination of all the other material repre- 

 senting the related species in the British Museum, enables me 

 now to assign it definitely to the genus Hyperacrius. Its relatively 

 large size and, as regards the parts influenced by the temporal 

 and masseter muscles, slightly less modified skull stamp the 

 species as being fundamentally a little more primitive than are 

 the other known species of Hyperacrius. But its palatal structure 

 is slightly more advanced, foreshadowing the structure so char- 

 acteristic of the higher voles; its highly modified mole-like 

 fur, completely concealed ears, and lengthened fore-claws, are 

 important specializations for underground life, specializations 

 which afford a parallel to those seen in Ellobius. In this connec- 

 tion the presence of two colour phases in H. wynnei is of great 

 interest; for just such a variability of colour has long been 

 recognized as one of the most conspicuous characters of at least 

 the best-known species of Ellobius, viz.. E. talpinus. The light 

 colour phase of H. wynnei is no doubt equivalent to the normal 

 pelage of most other voles. The dark phase might perhaps be 

 regarded as a partial melanism, but in my opinion it is susceptible 

 of another explanation. It bears such a close resemblance to 

 the normal dusky youthful pelage found not only in other species 

 of Hyperacrius, but in the young of many (or most) other Micro- 

 tine genera and it is so little like an ordinary example of melanism, 

 that it seems reasonable to suppose that we have in this dusky 

 pelage one of those rare instances of the life-long persistence of 

 characters normally peculiar to infancy or adolescence. Quite 

 possibly this very tendency to retain the dark immature colora- 

 tion throughout life is to be regarded as a result of subterranean 

 habits; deprived of the light stimulus the normal bright adult 

 colour fails to appear in many individuals at the appropriate 

 moment and such animals thereafter continue to wear the dusky 

 coats of the young and probably of the ancestral forms. 



According to the field notes of Major H. H. Dunn, who pre- 

 sented a specimen to the British Museum, this species has " mole- 

 like habits and it is found in grass ground in the pine-forests " 

 at an altitude of 7000 feet. Quite probably the normal habits of 

 this species are strictly subterranean, and if so further search 



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