. A manual of zoology. PHYLUM MOLLUSCA 265 1. THE PELECYPODA A Fresh-water Mussel will serve as a convenient example of the Fresh-water mussels are found in rivers and lakes in most parts of the world. Anodonta cygnea, the swan-mussel, is the commonest species in England; but the pearl-mussel, Unio matgaritifer, is found in mountain streams, and other species of the same genus are universally distributed. Unio complanatus is the common fresh-water pearl-mussel in the Eastern United States, and Anodonta fluviatilis represents the European A. cygnea. (t. Fig. 158. —Anodonta cygn
. A manual of zoology. PHYLUM MOLLUSCA 265 1. THE PELECYPODA A Fresh-water Mussel will serve as a convenient example of the Fresh-water mussels are found in rivers and lakes in most parts of the world. Anodonta cygnea, the swan-mussel, is the commonest species in England; but the pearl-mussel, Unio matgaritifer, is found in mountain streams, and other species of the same genus are universally distributed. Unio complanatus is the common fresh-water pearl-mussel in the Eastern United States, and Anodonta fluviatilis represents the European A. cygnea. (t. Fig. 158. —Anodonta cygnea. The entire animal. A, from the left side; B, from the posterior end. d. p. a, dorsal pallia! aperture; e-r. spA, exhalant siphon; ft. foot; in. sp/i, inhalant siphon; lg, ligament; m. mantle; um, umbo. (After Howes.) The mussel (Fig. 158) is enclosed in a brown shell formed of two separate halves or valves hinged together along one edge. It lies on the bottom, partly buried in the mud or sand, with the valves slightly gaping, and in the narrow cleft thus formed a delicate, semi-transparent substance (m) is seen, 1 The earlier and quite as appropriate name of this class is Lamellibran- chiata.—AMERICAN Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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