 There is sexual dimorphism on the border of the rib shield of the operculum, which is straight in females, but curved in males.Aberrations in the shape of operculum have been observed.In a specimen from Vouvant in France, and another from a spring near Bar in Montenegro, a double rib was present, but the rib shield was reduced; in a specimen from Ohrid Lake, only the rib shield was reduced.