More or less compressed and sub-triangular, without grooves; byssus very large and much developed; summit entirely terminal and anterior; smooth and radiated with blue or purple, covered with a dark brown epidermis; inside margin blue, shade decreasing to the centre.
M. crenatus. The crenated Mytilus.
Species longitudinally grooved, radiated, or striated.
M. hirsutus. The bearded Mytilus.
Species with grooves; covered with a shaggy or bearded epidermis.
2. Modiola. Twenty-three species.
Taken by Lamarck from the Mytilus, as it differs by being more transverse than longitudinal, and the beaks, instead of being terminal, are placed beneath the apex.
Shell smooth, sub-transverse, equivalve, regular, sub-triangular, the posterior side short; summits almost lateral; hinge lateral and linear, without teeth; ligament partly interior, placed in a marginal furrow; one sub-lateral elongated muscular impression in each valve.
Modiola Papuana.
M. tulipa.