equilateral, integropaleate, thick and heavy. The shape is oval
in juveniles and tends to be near triangular in adult specimens.
The surface has well marked concentric and regular sulca
tions. The number of sulcations in 5 mm of shell appears
to be independent of age and varies between four and eight,
specimens with five or six sulcations being most frequent
(Table 1, Fig. 4A). The hinge is typically heterodont with
three cardinal teeth on each valve, and two crenulate lateral
teeth, simple in the left valve and double in the right one.
In the Miño River population the number of denticles per