Among ribs between the axilla and groin, the axillary rib corresponds to the axillary groove, and the other ribs correspond to the costal grooves (this photograph indicates 11 costal grooves).

In this species, the number of costal grooves between the axilla and groin, omitting the axillary groove, is 10-12, modal number being 11. The relative frequency of 12 costal grooves is much higher in some of 19 localities examined (e.g., 23 of 34 males, three of four females, Ohmagari-shi, Akita Prefecture; 23 of 48 males, seven of 12 females, Minakami-machi, Gunma Prefecture).