A useful difference between the skulls of the weasel ( Mustela nivalis ) and the stoat (M. erminea). The index L/B ( L = palatine length; B = smallest palatine width) is suggested to discriminate between weasel and stoat. As a working hypothesis, the boundary between the species is laid at L/B = 4.0; for the weasel, L/B > 4.0, while for the stoat L/B < 4.0. Based on this hypothesis it is supposed that the Mustela from Corsica belongs to M. erminea, not to M. nivalis.