14 



PROTECTION OF FRESH-WATER MUSSELS. 



The first two columns show the limits of size for each lot used, the 

 greatest diameter being the basis of measurement. 



The third column shows the approximate number of pairs of shells 

 composing a ton, the unit of purchase ; multipljdng this number by 2 

 would give the number of single shells per ton. 



In the fourth column there is given, in the case of the critical 

 sizes, the number of 18-line blanks readily taken from a single shell 

 (which is one-half the number yielded by a pair of shells, or an indi- 

 vidual mussel). 



The fifth column indicates the number of gross of blanks, by com- 

 putation, yielded by a ton of shells. This computation is based upon 

 the cutting of 18-line blanks (not the larger 20-line blanks that have 

 been taken from some of the larger shells in the illustration). Some 

 of these shells are cut excessively close to the tips, on account of 

 taking too many larger line blanks. It must be understood that dif- 

 ferent sized shells are adapted for different lines of buttons. The 

 data herein is for comparative purposes only. 



Table of Sizes, Weights, and Button Production for Niggerhead Shells 

 (Approximate Figures). 



o At the time of making this table only a few of the larger-sized shells were available, so the estimates 

 ol blanks are less accurate. 



It may be seen from the table that a marketable ton of nigger- 

 heads could be composed of the shells of 3,200 or of 33,000 mussels, 

 according as the shells were 4 inches in length or only 1^ inches. As a 

 matter of fact, no marketed ton is ever composed of mussels of an 

 exactly uniform size; furthermore, the extremely large niggerhead 

 shells are very rare and generally not very desirable on account of 

 inferior quality and disproportionate waste. A ton of shells from 

 a region of depletion will also include a number of the smallest and 

 not strictly marketable shells. 



