A Conchological Manual - 1842 Author:George Brettingham Sowerby Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: INTRODUCTION. 11 HABITS—Land, Fresh-water, or Marine Shells. Another distinction, leading to important results in classification, is that which is derived ... more »from the nature of the element breathed by the Mollusc. And although this consideration belongs more especially to the study of the animal itself, yet the habits of the animal materially influence the structure of the shell. The Terrestrial or Land Molluscs live on land, breathe air, and feed on plants and trees.—Those who find pleasure in horticultural pursuits will at once call to mind a too familiar example of these Molluscs in the common garden snail. The Land-shells are all univalves, and constitute a family in the Lamarckian system under the name " Colimacea," or snails, corresponding with the Linnean genus Helix.—They are generally light in structure and simple in form. The Aquatic, or Fresh-water Molluscs, such as the Planorbis, commonly called the Fresh-water Snail; the Unio— known by the name of Fresh-water Muscle, is found in ponds, ditches and rivers. The epidermis of these is generally of a thick, close-grained character, and they are subject to corrosion near the umbones. There are but few genera of fresh-water shells besides the Uniones, among bivalves, and the " Melaniana" among univalves. Concerning the former it may be observed, that they are all pearly within, and the colour of the thick horny coating embraces all the varieties of brownish and yellowish green. The Marine, or sea-shells, belong to all the classes and orders, and include by far the greater number of species. They vary in the habits of the animal, and consequently in the situations in which they are found. Some are found buried in sand and marine mud, and are named " Arenicolce" or inhabitants of sand; others in holes of rocks and ...« less