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THE PEARL
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in
the present regardless of the future, but these are gradually being
made amenable to restrictive laws as authorities awake to the value of
the industry. A greater danger which threatens the unio of American
streams, is the pollution of the water by the discharge of the refuse
of factories and the sewage of cities into them. A mussel bed will
recover in time when denuded by fishers, but sewage and poison kills it
out entirely.
Although
fresh-water pearl-bearing mussels are found in the streams of many
countries, only in the United States are they taken in sufficient
quantities to make the fishings important as an industry. They are to
be found throughout the Mississippi drainage area and in part of that
of the St. Lawrence. Few exist on the Pacific coast and those of the
Atlantic coast are generally inferior as pearl mussels. There are many
varieties of the unio which yield pearls. Latin names are given by
different writers to distinguish them, but as scientists differ in
their classifications, the names are not always uniform and are not
sufficiently well established to be useful, descriptively, to the
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