we can scarcely believe that it can possibly be withdrawn into the shell; yet this is easily effected, and that so completely, that the closely-fitting operculum is seen, shutting the aperture considerably within the margin. It is performed, however, if I may judge from my own experience of several British species, with some difficulty, and by a succession of efforts; and the animal when once forced by annoyance to retire, is often ill-disposed to protrude again, at least for a considerable time.
NATICA.
The species of the genus are widely distributed, and are most numerous within the tropics. Several of them are of large size. Seven or eight species are found on the British shores, of which the finest is Natica monilifera.
In this large and handsome shell, the form is globose, nearly as broad as long; it is strong but not solid, smooth and glossy, though with a few fine sunken lines, which mark the progressive growth. The ground-colour is whitish, sometimes tinged with flesh-red, or with bay, and each whorl is marked along its upper margin with a line of oblique but parallel dashes of rich chestnut.
