_M. stultorum._ The fool’s Mactra. Pl. 9, fig. 6.
Species in which all the teeth are very large, lamellous, striated longitudinally; colour reddish brown.
Species thick, solid, without epidermis; lateral teeth finely striated.
_M. trigonella._ The three-cornered Mactra.
Species in which the lateral teeth are almost obsolete; exterior surface smooth.
_M. triangularis._ The triangular Mactra.
Species very small, strong, opaque, white; inside white; margin strongly crenated.
Species very thick, solid, striated longitudinally; the cardinal teeth obsolete, or almost so; the lateral very thick, very close, and reflected; an external ligament as well as an internal one.
May be easily known from the Mactra and Lutraria, as the valves, when closed, fit exactly, and do not gape. It is remarkable that all the living species contained in this genus only exist in the seas of Australasia, while at least seven species in a fossil state are found in France.
Shell inequilateral, sub-orbicular, close, equivalve, sometimes attenuated at one end; two divergent primary teeth, with a cavity at the side; lateral teeth obsolete; ligament internal, inserted in the cavity of the hinge.
Crassatella Kingicola. C. donacina. C. sulcata. C. subradiata. C. contraria. C. cuneata. C. rostrata. C. glabrata. C. erycinæa. C. cycladea. C. striata.
_C. sulcata._ The furrowed Crassatella. Pl. 6, fig 4.
Shell ordinarily thick, striated transversely, denticulated, sub-triangular, equivalve, inequilateral, summits well marked and evidently turned forward; hinge very large, subsimilar, formed by two diverging cardinal teeth, separated by a large pit; ligament almost entirely interior, and inserted in the pit.
_C. Kingicola._ The King’s Island Crassatella.
Ovate, orbicular; yellowish white, with obsolete rays; very minutely striated transversely; the umbones somewhat plicated.
The only living species of this genus is found on the sand in New-Holland, but there are many fossils in France. It is so equivocal in character that it is difficult to judge of their hinge.
_E. cardioides._ The cardium-shaped Erycina. Pl. 6, fig. 5.
Shell rather longer than high, sub-triangular, regular, equivalve, inequilateral, rarely gaping; the summits well marked and a little anteriorly inclined; hinge subsimilar; two unequal cardinal teeth, converging at the summit, and leaving a pit between them; two lateral teeth, not distant, lamellous, inserted; ligament interior, fixed in the cavity between the primary teeth.