The royal natural history . umerous kinds of fresh-water mussels (Unionidce and Mutelidce) occurin the lakes and rivers of all continents, and the large islands of the MalayArchipelago and New Zealand; although in most of the smaller islands they BIVAL VES. 4r are unknown. North America, and especially the drainage-area of the Mississippiand its tributaries, is the great home of the Unionidas. The species maybe counted by hundreds, some being the most remarkable and beautiful thaiexist in any part of the globe. The shells are usually equivalve, and joined byan external ligament, but exhibit gr
The royal natural history . umerous kinds of fresh-water mussels (Unionidce and Mutelidce) occurin the lakes and rivers of all continents, and the large islands of the MalayArchipelago and New Zealand; although in most of the smaller islands they BIVAL VES. 4r are unknown. North America, and especially the drainage-area of the Mississippiand its tributaries, is the great home of the Unionidas. The species maybe counted by hundreds, some being the most remarkable and beautiful thaiexist in any part of the globe. The shells are usually equivalve, and joined byan external ligament, but exhibit great variation in shape. The hinge is sometimes destitute of teeth (Anodonta, Mycetopus); or powerfully formed withstrong complex interlocking teeth, as in many of the North American forms; orit may consist of very numerous teeth on a straight hinge-line (Pliodon),recalling the form of hinge obtaining in the Arcidce. The exterior is covered witha thick, often glossy periostracum, varying in colour, the prevailing tints being. LARGE KIVER-MUSSEL, A iLuilnnIn cygnm (nut. size}. greenish olive, brownish yellow, brown, and black. Many are beautifully rayedwith green. The solidity of many of the species—especially the North Americanforms—is remarkable, although others are thin and fragile. Some are pearlywithin, and others white, pinkish purple, salmon-colour, yellow, or shells are marked with two adductor scars, and the pedal scars are also oftenclearly visible, while the pallial line is uninterrupted by a posterior sinus. Theanimal of Unio has the lobes of the mantle free, excepting posteriorly, wherethey are connected, forming two orifices, the lower or branchial for the passage ofthe water to the gills, and the upper for excretal purposes. The former isfringed with several rows of papillae. The foot is large, thick, tongue-shaped,and used as a creeping and burrowing organ. The sexes are united in theEuropean species, but distinct in the American. A remarkable f
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
