The Collaborative International Dictionary of English v.0.48:

Arvicola \Arvicola\ n.
   a genus of mice in some classifications considered synonymous
   with Microtus.

   Syn: genus Arvicola.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Microtus
    n 1: voles of the northern hemisphere [syn: Microtus, genus
         Microtus]