bring
about twice as much, muckets half that price, and the other varieties
together will average about twenty-five per cent, more than
nigger-heads, though among these the deer-horn is worth about four
times as much as the nigger-head.
In
the first six months of 1898 nearly four thousand tons of mussel shells
were sold by mussel fishermen on the Mississippi. They brought about
thirty-nine thousand dollars, 94 per cent, of these were nigger-heads.
The
spawning time of the unio varies with different species. In the central
Mississippi basin it is normally February, March and April for
nigger-head, and summer and early fall for the mucket and sand-shell.
The
unio is a slow growing animal. Under normal conditions it takes ten
years for a nigger-head to reach a size of three inches; fifteen to
eighteen years to attain a shell diameter of 4^ inches. This
corresponds very closely with the life of the meleagrina, though the
shell of the latter ceases to grow in size at about eight or ten years.
After that it continues to lay on thickness up to eighteen or twenty
years.
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