FRESH-WATER MUSSELS AND MUSSEL INDUSTRIES. EZ 
An excellent illustration is afforded by the fat mucket. It is the most common 
shell of the lakes of the upper portion of the Mississippi Basin, but in these localities it 
is nearly always very thin, sometimes almost papery. In parts of the upper Mississippi 
it attains a large size, and has a shell of good quality and thickness except for the rela- 
tively thin tip (the hinder portion of the shell). In Lakes Pepin and St. Croix the same 
species is not only of the best quality, but of such degree of uniformity in thickness as 
to be practically tipless.¢ 
A shell can not always be judged by its appearance. The Bureau, having a shell- 
testing shop at the Fairport station, makes a practice of testing out the shells submitted 
by the field parties. Pocketbook shells of exceptionally fine appearance received from 
the Sauk River proved upon test to be so brittle as to be worthless. Niggerhead shells 
collected in some lowland waters along the Mississippi in Louisiana had an appearance 
of first quality, but in the cutting test showed a chalky character and a tendency to 
split, which gave them a second-grade rating. It happens, too, that a shell having a 
nacre which is white upon the surface may be found in process of finishing to be dis- 
colored beneath. 
Besides the useful shells, there are found in all rivers, but not in any uniform pro- 
portion, those which are useless on account of being too thin or discolored. Some of 
the most beautifully colored shells are of no commercial value. 
VARIETIES OF COMMERCIAL SHELLS. 
Most of the commercial fresh-water mussels, considered with regard to the quality 
of shell, fall into two main classes, which may be termed the Quadrula class and the 
Lampsilis class, giving to each class the name of the genus to which belong most of the 
common species exhibiting the characters of the class. There remain a few groups of 
species of less importance, which have little in common with the others and which may 
be classed together under the head of “Miscellaneous groups.” Each class naturally 
divides itself into several groups, which may be conveniently designated by the name 
of the principal species of the group. It is rather significant that the classes and groups 
correspond approximately to the general plan of scientific classification. Mussels close 
in systematic relation possess, roughly speaking, similar qualities of shell, but this must 
not be taken as a universal rule. For our present purposes, we are not primarily con- 
cerned with the scientific classification, but it happens conveniently that general state- 
ments can be made regarding the natural history of the mussels of some of the respective 
groups. 
In view of the large number of species used more or less for commercial purposes 
in the manufacture of buttons or novelties, it is somewhat difficult to decide which species 
to include. Especially is this the case since a number of mussels useless to the manu- 
facturer have an importance in the production of pearls. In the following pages several 
species are discussed which are not at present of known economic importance, but it is 
believed that none is mentioned that is not familiar to fishermen in one region or 
@ In the terminology of pearl-button manufacture a tip isa blank (unfinished button) less than one-twentieth of an inch in 
thickness, or that portion of the shell from which only blanks of such thinness are cut. In an ordinarily good shell not more 
than one-fourth of the area of the shell is tip. If the thickness of a shell is unusually well sustained in the hinder portion, the 
shell is without tip; at the other extreme a shell is spoken of as all tip, and such a shell isofno value. However, the term “tip” 
is somewhat differently employed by some manufacturers. 
