Gregariella Monterosato, 1883. Type species (M): Modiolus sulcanus Risso, 1826, non Lamarck, 1805, = M. barbatellus Cantraine, 1835, Mytilus petagnae Scacchi, 1832. Recent, Mediterranean. Botulina Dall, 1889. Type species (M): Modiola opifex Say, 1825. Recent, eastern Atlantic. Shell elongate, inflated. Umbones incurved, orthogyrate. Anterior end smooth or with commarginal ribs; posterior end with radial riblets, hirsute behind keel. Hinge plate weak, with dysodont teeth. Ligament opisthodetic, external. Inner shell margin crenulate. The genus is similar to Musculus, with a hirsute periostracum and crenulate interior shell margin. The name is derived from the Latin gregarius, living in flocks; gender is feminine. This genus is known from as early as the Carboniferous. We appreciate the advice of Karl H. Kleemann on this genus. Literature: Kleemann (1986b), B. Morton (1982c), Nielsen (1976), Palazzi (1981).