260 MICROTIN^ 



a suspicion of mouse plague, it is only too easy to collect a very 

 long series of specimens, the oldest of which is scarcely adolescent. 

 In another district, where breeding has slowed down for a time, 

 subadults may form the great bulk of the catch. Elsewhere, 

 after temporary cessation of breeding, the series will consist chiefly 

 of adult and sometimes of aged animals. The result is that three 

 separate parcels of voles come before the systematist on different 

 days; each represents a definite locality, and each possesses a 

 definite character of its own, the individuals in each parcel form- 

 ing a very uniform series. Small wonder that the systematist 

 hastens to describe each batch as it arrives as a new species. But 

 on the day of revision the contents of all the parcels come together 

 before the reviser. For a long time he struggles to make a " key " 

 to the characters of the described forms ; but the characters cannot 

 be ■■ keyed," and it becomes evident that there is something 

 wrong. Throwing the lot into a heap the reviser begins by deter- 

 mining the relative ages of the skulls of all the specimens, and 

 as they arrange themselves in order of length he sees at last that 

 he is not dealing with so many distinct species and subspecies 

 but with so many different stages of growth. That is exactly 

 what has happened in the present case. 



E. (Phaulomys) smithii was based upon a young male, obtained 

 in February 1904; by accident the fifty-three specimens of the 

 series collected in Hondo, Kiushiu, and Shikoku, by M. P. 

 Anderson in the following year are all young too. The condylo- 

 basal length in the largest of them is only 24-5 mm., and in all, 

 the skull is like that of an ordinary Evotomys, the teeth stamped with 

 the peculiarities of young E. rufocanus, and vigorously growing. 



Later on Mr. Anderson collected thirteen in Hokkaido. The 

 majority of these are adult, some even old ; in size, skull form, 

 and tooth pattern they are strikingly different from the material 

 referred by Thomas to E. smithii. These were therefore described 

 as a new species, E. (Craseomys) bedfordice. But two specimens of 

 this original series of E. hedfordice are immature, and these are not 

 distinguishable from the material upon which E. smithii was 

 founded. 



In the same paper E. (C) andersoni was described, from two 

 specimens obtained in North Hondo, as " very like bedfordice 

 externally, but with longer tail, and much less powerful teeth." 

 Both specimens, however, are merely large adolescents, inter- 

 mediate in age between the adult material upon which E. bedfordice 

 was established and the immature material referred to E. smithii 

 — hence the less powerful teeth as compared with E. bedfordice. 

 As regards the length of the tail, there is nothing in that ; for later 

 specimens from Hokkaido show that in E. bedfordice the tail may 

 measure 58 mm., and it is only 54 in E. andersoni (as in the 

 type of E. smithii). Lastly, Anderson's E. niigatce also has been 

 founded upon an adolescent animal ; its tail, though long, averaging 

 about 61 mm. in a series of seven, can be matched quite well in the 



