The Plague of Field Mice, by Sir Walter Elliot. 467 



tine with much care, agrees with me, in considering the agent in 

 both these instances to have been A. arvalis, the commonest 

 species in Syria. 



The ubiquity of the field vole, ranging from the sea level to 

 4,000 feet of elevation in this country, and much higher in con- 

 tinental mountain ranges ; their readiness to adapt themselves to 

 such vegetable food as offers ; their consequent diversity of habit ; 

 and the variations of size and colour observable among them, 

 when congregated in numbers ; have given rise to a multiplica- 

 tion of species, established on specimens presenting only slight 

 peculiarities. In the charming monograph of the Swiss Arvico- 

 lince, by V. Fatio, already referred to, these are reduced to five, 

 each associated with numerous synonyms, as follows : — 



1. A. glareolus, Schreber, 1775-92, with 13 synonyms. Illiger 



has formed it into a separate subgenus {Hypudceus) dis- 

 tinguished by the molars having distinct roots. 



2. A. agrestis, L. Faun. Suec, 1746, with 10 synonyms. 



3. A. amphilius, L. Sys. Nat. xii., ed. 1766, with 26 synonyms. 



4. A. arvalis, Pallas, 1788 (the type campagnol of Buffon), with 



13 synonyms. 



5. A. nivalis, Martins, 1841, with 5 synonyms. 



At the same time M. Fatio regrets that his limits preclude him 

 from noticing other species in neighbouring countries, such as 

 A. ratticeps and A. campestris, of Blasius ; A. subterraneus and A. 

 Savii, of De Selys ; and A. socialis, of Pallas, from the Yolga. 



These, with some others, have been formed into a subgenus, 

 or group, characterised by the smallness of the ear, and hence 

 named Microtus, an exhaustive examination of which, has been 

 made by Prof. L. H. Jeitteles, in a paper read to the E. and I. 

 Zoological and Botanical Society of Vienna, on the 7th of July, 

 1876, in which he comes to the conclusion that they all belong to 

 one and the same species, inhabiting the plains, and to a con- 

 siderable elevation, the mountains of Central Europe, Italy, and 

 Spain, and he is sure that they will be found also in Greece and 

 Turkey. He attaches little value to most of the characters on which 

 these distinctions were founded, such as the number of mammae, 

 the presence of additional ribs, the proportionate length of the tail, 

 the denned separation of colour between the back and belly. 

 The only constant mark that he recognises is the number of 

 tubercles or pads on the sole of the hind foot, which are five in 



