54 



MICEOTIN^ 



that of genera like Microtus. Among other voles {Mimomys, 

 Arvicola, Pitymys, Microtus, etc.), with the exception of Orthri- 

 omys and Herpetomys, the possession by m^ of three closed 

 triangles only, on the one hand, or of four or more on the other, 

 has been a distinction of generic importance since Pliocene times 

 at least; but in Phenacomys both types of m^ are associated, 

 and the distinction between them, if it be of any systematic value 

 at all, is of no more than specific importance. Ancient species 

 of Phenacomys, in which the outward characters may have been 

 a little more primitive, those parts of the skull under the direct 

 influence of the temporal muscles a little less modified, and 



a little less reduced than they are in the living species of 



this genus, may thus well have been the ancestors common to 

 both Pitymys and Microtus, with their respective adherents; 

 indeed, such forms may well have been ancestral to all the 



Fig. 26. — Cheek-teeth of Pitymys subterraneus de Selys-Longchamps. 

 Crown views : a. right upper, b. left lower molars. 



other known voles as well. Unfortunately, nothing is at present 

 known of the palaeontological history of Phenacomys. 



Pitymys is an ancient genus, now widely distributed in 

 Central and Southern Europe and in South-eastern North 

 America. The earliest remains are apparently those obtained 

 from the later Pliocene (Cromerian Beds) of Britain; these 

 consist of teeth and fragmentary lower jaws, indicating the 

 presence of several species, which in size and form agree in all 

 essential respects with the teeth and lower jaws of recent Pitymys. 

 But whether these ancient fossils belonged to Pitymys, as 

 we now understand it, or to Neodon, Tyrrhenicola or some other 

 genus, cannot be determined with the material at present 

 available. 



The living members of the genus are small voles with very 

 small eyes, small ears, short tails, and soft, short, dense and 

 more or less mole-like fur. They have large hands provided 

 with rather long claws, relatively short feet with claws rather 

 shorter than those of the fingers, moderately hairy soles and 



