O. imbricata. The imbricated Oyster.
Species orbicular and plaited.
O. crista-galli. The Cock’s-comb Oyster.
Species strongly plaited longitudinally.
3. Vulsella. The Tweezers. Six species.
This genus has several characteristics which distinguish it from the Ostrea; they are free; the valves and the apices are nearly equal, with a projecting callosity on each valve, depressed underneath, and obliquely arched for the reception of the ligament.
Shell sub-nacreous, sub-regular, sub-equivalve, inequilateral; upper valve finely granulated, or striated longitudinally from the apex to the margin; summits anterior, distant, recurved below; hinge without teeth; ligament undivided, thick, inserted in a rounded cavity, made in a slightly projecting callosity on each valve; muscular impression sub-central, rather large, and two very small ones entirely anterior.
V. lingulata. The tongue-like Vulsella. Pl. [15], fig. 6.
Elongated, depressed, transversely striated; pale yellowish brown, with longitudinal darker stripes.