From The Collaborative International Dictionary of English v.0.48 :
Arvicola \Arvicola\ n.
a genus of mice in some classifications considered synonymous
{Microtus">with {Microtus.
Syn: genus Arvicola.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
Arvicola
n 1: in some classifications considered synonymous with Microtus
[syn: Arvicola, genus Arvicola]