the
conch, a large univalve fountain-shell-fish (Strombus gigas), is a
native of the West Indies. Another, a gasteropod, the ear-shell
(Haliotis) known in the United States as the abalone, is found on the
coasts of California, Japan, the English Channel Islands and elsewhere.
The Californians are divided into three classes, the blue backs, about
six inches long, and green and red ears, which are half as large again.
Pinnas yielding black seed pearls are found south of the Island of
Mafia on the east coast of Africa. On the banks and shoals between
Mafia and Zanzibar is a red mussel from which white pearls are taken.
The
fresh-water pearl-bearing mussel, the unio, unlike the sea oyster is
most abundant north of 30 degrees N. In China and the Hawaiian Island
Oahu it is found a little to the south of 30 degrees N., and it has
been discovered lately in Southern Rhodesia a little north of 30
degrees S., but the countries and streams in which the unio is
plentiful and where it yields the most pearls lie within latitudes 30
degrees N. and 60 degrees N. They have been taken from the streams of
Great Britain
206
