FRBSH-WATER MUSSELS AND MUSSEL INDUSTRIES. 1 7 



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 w^hich 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« 

 cemed 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 is a 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 sheU 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 is of no value. However, the term "tip'* 

 is somewhat differently employed by some manufacturers. 



