general
reader. In treating of the various kinds of pearl-bearing unios of the
United States therefore in these pages, the common names by which they
are known will as a rule be used with the scientific names appended, as
revised by the department of mollusks of the United States National
Museum.
From
the times of Roman colonization until now, pearls have been taken from
the mussels of British streams. There are three varieties of
pearl-bearing mussels in Great Britain: Painter's mussel (U. pictorum),
the Swollen River mussel (U. tumidus) and the Pearl mussel (U.
margaritifera).
The
first two occur only in the streams and ponds of England and Wales and
the pearls found in them are of inferior quality. The latter inhabits
the streams of Scotland and the northern counties of England and to
some extent are found in Ireland and Wales also. The shell is oblong,
rather flat and heavy and about five and one-half inches long. The
exterior surface is rough, and blackish-brown; the pearly interior has
a tint of flesh color mottled by stains of dull green. It was from this
variety
255
