The flowers have a hollow tube at the base bearing at its free edge five sepals, an equal number of petals, usually concave or spoon-shaped, pink or white, and a great number of stamens.
The beak or umbo of each valve is prominent and rounded, and a number of sharp ridges and furrows radiate from the apex to the free edge of the shell, which is crenated.
This always begins at the place where the attached flagellum emerges from the body; and its free edge is really constituted by the latter, which forms a flageIlar border.
Fissure between the free edge water forms which carry the young in brood-pouches formed by the ctenidia have suppressed this larval phase.
The free edge of the left half of the mantle-skirt b is represented as a little contracted in order to show the exactly similar free edge of the right half of the mantle-skirt c. These edges are not attached to, although they touch, one another; each flap (right or left) can be freely thrown back in the way carried out in fig.
