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A History of British Mollusca, and Their Shells, by E. Forbes and S. Hanley
A History of British Mollusca and Their Shells by E Forbes and S Hanley Author:Edward Forbes General Books publication date: 2009 Original publication date: 1853 Notes: This is a black and white OCR reprint of the original. It has no illustrations and there may be typos or missing text. When you buy the General Books edition of this book you get free trial access to Million-Books.com where you can select from more than a million book... more »s for free. Excerpt: MYTILTDJE. The true Mussels are mostly inhabitants of the sea, a few only dwelling in fresh water. They have more or less elongated and very inequilateral shells, always, however, equivalve. The hinge is of a very simple structure, generally devoid of teeth ; the ligament is linear. The surface of the shell is smooth, or rugose, or obliquely striated and sulcated, and is often covered by an epidermis. The animal has always two adductor muscles and a narrow strap-shaped foot, furnished with a hyssal groove. It can spin a very strong and copious byssus, though, as in the case of the Litkodomi, this is in some species only done when it is young. The mantle has its edges variously united in some genera, and apart in others, so that some forms have distinct siphonal tubes and others none. Usually the anal tube is complete, and the branchial only rudimentary. The structure of the shell in the Mytilidee has been submitted to microscopic examination by Dr. Carpenter, with interesting results. He finds the shells of Mytilus, Hodiola. and Lithodomus all to possess a periostracum of horny membrane in which no distinct structure could be detected. Between it and the shells a thin layer of minute cells may frequently be observed. The shell itself presents two layers, distinguishable by their colour; the internal one is often iridescent and always nacreous. Neither layer in the two former genera presents very distinct organic structure, butin LitfMxlomus the external stratum has a remarkable tubular structure, resembling that of dentine. The shell of Dreissena has a very different organization. In it the internal ...« less