202 Lloyd's natural history. 



the true Mice, but are closely allied to the Hamsters {Cricetus)^ 

 of which there are no existing British representatives. 

 Although the Hamsters have rooted and tuberculated molars, 

 their tubercles, instead of forming three longitudinal rows, as in 

 the Mice, are arranged in two such rows. By the develop- 

 ment of such tubercles into prisms the root-less molars of the 

 Voles have originated ; and it is interestmg to notice that in 

 some of the extinct species of the latter these teeth, although 

 composed of the same prisms, are shorter and show more or 

 less distinct roots. We may accordingly regard the Voles 

 as forming a highly-specialised side-branch which has taken 

 origin from the Hamsters. 



Till within the last few years, the Voles have been almost 

 universally known by the generic name of Arvicola ; but it has 9 

 been discovered that the title under which they are here entered 

 antedates the latter by one year, and, therefore, by the rules of 

 zoological nomenclature, has to be employed. In this particular 

 instance the substitution of a strange name for one which had 

 become so well-known, is much to be deplored ; but it will be 

 obvious that if exceptions are once made in enforcing the rule 

 of priority in nomenclature, it cannot be logically maintained 

 elsewhere. 



I. COMMON FIELD-VOLE. MICROTUS AGRESTIS. 



Mus agrestis, Linn., Fauna Suecica, p. ii (1761). 



Mus gregarius^ Linn., Syst. Nat. ed. 12, vol. i. p. 84 (1766). 



Arvicola agresiis, Fleming, British Animals, p. 23 (1828); Bell, 



British Quadrupeds, 2nd ed. p. 323 (1874). 



Microtus agf-esHsj Lataste, Le Naturaliste, 1883, p. 349, id. 



Act. Soc. Linn., Bordeaux, vol. xxxviii. p. 36 (1884). 



{Plate XXIV.) 



Characters. — Size small ; tail one-third the length of the head 



and body ; soles of hind-feet with six naked pads ; colour of 



