Page:Natural History, Mollusca.djvu/180

 more of the character of the genus, the outer lip beginning to be bent in, or rather thickened, and the mantle beginning to secrete and to deposit the coat of enamel, which is studded with white spots. The figure displays this state: the spire is sinking behind the elevated lips, which are thickening; while the spotted coat is seen at one side, creeping along over the back of the shell, which it is destined to cover.

At length the thickening of the lips proceeds to such an extent as almost to conceal the spire, and to reduce the aperture to a narrow line, the edges of which are now thickly plaited with the tooth -like ridges so characteristic of the genus. The lobes of the mantle protrude through this aperture, and expanding on each side, have deposited all over the exterior of the shell a coat of glassy enamel, studded with pale round spots, which entirely conceals the transverse bands that were formerly visible across it. The appearance, therefore, is now such as is represented in the following figures, which most of my readers will readily recognise as those of a familiar shell.

The deposition of enamel is the last process of