The New Student's Reference Work/Unio

U′nio, the name for a number of freshwater mussels very abundant in the United States. Their name would indicate a single shell, but they are bivalves. For their structure see Clam. Some forms, especially in the streams of Wisconsin, Ohio and New Jersey, contain pearls. These animals are gathered in great numbers, but the pearls are of infrequent occurrence and mostly small. Occasionally, however, those valued as high as $500 to $2,000 have been found. The shells are used for making pearl-buttons.