On the systematics of some Recent Rissoa (Gastropoda, Prosobranchia)

The following Rissoa species are discussed: R. splendida. Differs from R. ventricosa in being less slender, because the sculpture has been reduced to a few weak spiral grooves on the bottom of the shell, and also in showing a darker colour pattern. Adriatic Sea and eastern Mediterranean, far from rare. R. variabilis. Exhibits the larger type of apex. Far from rare in the entire Mediterranean. The forma spongicula is considered a slender form, perhaps even a subspecies, from the Golfe de Gabès in Tunisia. R. ventricosa. Exhibits the smaller type of apex. The sculpture consists of spirally arranged small pits. Far from rare in the western Mediterranean and the Adriatic Sea. R. violacea. Exhibits the smaller type of apex. May be divided into two subspecies. R. v. violacea is not rare in the entire Mediterranean and is characterized by a marked violet spiral colour-band. R. v. lilacina is locally common along the European Atlantic coast and in the North Sea and lacks the colour-band. Intermediates between the two forms are known from Getarès, a few km S. of Algeciras. R. rufilabrum and R. porifera should not be considered separate species as long as insufficient factual data are available. So far the known facts lead one to conclude that there exists a somewhat irregular cline from a violet form in SW. Great Britain and Ireland to a form with shells that are less colourful, ribless or with a tendency to a reduced number of ribs, in Scottish, Danish and Scandinavian waters. Attention is drawn to the phenomenon of smaller and larger apices in the genus Rissoa.