Mya arenaria. Ten camera outlines of shells varying in length from 0.4 mm to 7.5 mm. They are intended to illustrate the change from a rounded outline in smaller individuals to the elongated condition of older forms. There is at first a more rapid posteri

Description:

Mya arenaria. Ten camera outlines of shells varying in length from 0.4 mm to 7.5 mm. They are intended to illustrate the change from a rounded outline in smaller individuals to the elongated condition of older forms. There is at first a more rapid posterior, and subsequently a more rapid anterior, growth of shell, which causes the relative position of the umbo to shift forward, and then back to a position midway between the two extremities of the shell.