Microtus subterraneus and M. multiplex are now thought to be two different species. M. subterraneus has more chromosomes (52) than M. multiplex (46 or 48). Lab-bred hybrids have lower fertility, and naturally occurring hybrids have never been found despite their distinguishable karyotypes. Salvioni analysed eight morphometric variables using a Nikon measure-scope (precision 1/1000 mm) and dial callipers (accuracy 1/100 mm). 288 specimens were collected in the Alps, Jura, and Tuscany. This uncommon data set assessed 89 specimens' chromosomes to establish species. 199 specimens only have morphometric data. We'll compare two species' skulls by classification which will help us to know how the skulls are different from each other.