Читать книгу The Book of the Pearl. The history, art, science, and industry of the queen of gems онлайн

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Pearls are yielded by various species of Unionidæ or Naiades occurring in the rivers of America, Scotland, Saxony, Bavaria, Norway, Sweden, Russia, France, China, etc. These mollusks exist exclusively in the fresh-water streams, lakes, and ponds, and quickly die when submerged in salt water. The Unionidæ are of particular interest in America, as it is here that this group is most abundant, and nearly every stream east of the Rocky Mountains contains more or less of them. The Mississippi basin abounds in Unios, or “clams,” as they are known to the fishermen of that region, and furnishes about 400 of the 1000 recognized species of this important family.

The Unios are most abundant in clear, running water, where the bottom is gravelly or sandy. The interiors of the shells are iridescent, and vary greatly in tint, exhibiting many delicate shades of color from silvery white to straw color, pink, purple, brown, etc.

About five hundred species of American fresh-water mussels have been recognized by conchologists. Many of these differ from one another so very slightly that they are scarcely distinguishable from an examination of the shells themselves, or even from the descriptions, and a detailed index to the complete list is of little economic importance. The professional fishermen and the shell-buyers take the trouble to name only the species with which they deal, which includes only about twenty-five species, all of which are margaritiferous, though some to a greater extent than others. In the pearling regions a popular nomenclature exists, the names given by the fishermen having reference to the shape, color, etc.