Page:Natural History, Mollusca.djvu/176

164 posterior part of the foot of the animal, and fitting the interior of the mouth of the shell when the animal retreats within the cavity.

The most important difference between the animals of this order consists in the presence or absence of a canal, formed by a lengthening of the lung-chamber of the left side, which is carried along a similar canal in the shell, or through a simple notch, to enable the animal to respire without the need of quitting its shelter. The presence or absence of an operculum is also a distinction; and the filaments, fringes, and other ornaments, which are occasionally carried on the head, the foot, and the mantle, afford other characters for the subdivision of this extensive Order.

(Cowries.)

Of this extensive group of shells, the majority of which are so exquisitely beautiful that they form the ornaments of cabinets, and the pride of collectors, a single British species is a sufficient warrant for noticing, in this volume, so attractive a family. Most of them are inhabitants of the tropical seas, residing chiefly near the shore, on reefs, and among rolled masses of broken coral; hence archipelagos and smaller groups of islands are peculiarly rich in the lovely Cowry-shells. There the brilliancy and variety of colour displayed both by the shells themselves and by the animals, accord with the glories of those latitudes, where the light and heat of a vertical sun give the greatest stimulus to animal and vegetable life.