A revision of the genus Revoilia Bourguignat 1881 (Prosobranchia: Pomatiidae)

The group here dealt with includes several species previously attributed to Otopoma Gray 1850. The shells are small to medium sized prosobranchs inhabiting eastern Africa, southern Arabia, the island of Socotra and, by extenston, a small area in western India. Their distribution and synonymy are reviewed and it is concluded that eleven species exist in two subgenera, Revoilia s.s. and Socotora Pallary 1925. Some previous authors have relied on the shape and size of the umbilicus as a specific indication, but our studies indicate that this, depending on the degree of callous closure, is merely a function of age and environment.