FRESH- WATER MUSSELS. 115 



calcium carbonate, and 3K per cent organic matter, it also contains other minerals in 

 very small proportions, less than i per cent each, such as silica, manganese, iron, alumi- 

 num, and phosphoric acid. It does not follow that because these minerals, other than 

 calcium, occur in minute proportions, they are any the less essential to the welfare of 

 the mussel; iron forms a very small proportion of the human body, but man can not 

 live without it. So these minerals may, then, be just as essential to the formation of 

 good shell as calcium, but with the possible exception of manganese it is probable that 

 all natural waters contain a sufficient quantity of the minerals to satisfy the needs of 

 mussels. Nevertheless an interesting and important problem may be found in a com- 

 parative study of the mineral content of different waters which yield shells of diverse 

 qualities. It is even possible that an excessive proportion of certain minerals in water 

 tends to the formation of shells that are brittle, discolored, or otherwise inferior. 



The sundried meats of mussels from the Mississippi River when analyzed have 

 been found to contain, besides moisture (about 7.6 per cent), protein (calculated from 

 nitrogen), 44 per cent; glycogen, about 9 per cent, ether extract (presumably fats), 

 a little less than 3 per cent; and undetemiined organic material, 13 per cent. The 

 remainder is mineral matter (chiefly phosphoric acid), 9 per cent; calcium (calcium 

 oxide), 8 per cent; silica, 3X per cent; manganese, about one-half of i per cent; and 

 such other minerals in small proportions as sodium, potassium, iron, and magnesium 

 (Coker, 191 9, p. 62, analysis by U. S. Bureau of Chemistry). 



As previously indicated, nearly all natural waters, at least those fed largely with 

 surface drainage, probably contain certain quantities of the required minerals, but it 

 would be going beyond the bounds of present knowledge to say whether or not the 

 abundant growth of mussels in certain streams and the variable qualities of shells 

 produced in different streams are related to the proportions of minerals present other 

 than calcium. Certain it is that a deficiency of lime is very unfavorable. The soft 

 waters of the Atlantic slope support very few mussels and these are small in size and 

 possess thin shells which are usually badly eroded. The thinness of the shells is asso- 

 ciated with the deficiency of calcium in the water, and the erosion is an indirect result 

 of the same cause, since the free carbonic acid, which attacks and consumes the shells 

 wherever the protective horny covering has been broken by abrasion, would, in harder 

 waters, be combined with the calcium in solution to form the bicarbonate. 



Circulation, of course, plays a great part in making available to mussels the dissolved 

 content of the water. It may be due not so much to low calcium content as to inadequate 

 circulation that small lakes and ponds in States of the Middle West generally yield 

 mussels with thin or dwarfed shells. 



The waters of many streams of the United States have been subjected to analysis 

 by the United States Geological Survey (Dole, 1909). The summarized analyses for 

 several streams, or parts of streams, productive of mussel resources, and for 10 others 

 that are not productive of commercial shells, are given in Table 9 below. It appears 

 that, within broad limits, the variations in content of silica, iron, magnesium, sodium, 

 and potassium are not significant as affecting productiveness (unless, as may be the 

 case, the quality of the shell produced is affected). Particular attention may be directed 

 to the columns of turbidity, calcium, carbonate radicle, and nitrate radicle. The 

 nonproductive streams, or parts of streams, listed are generally either very high in 

 turbidity or very low in calcium, bicarbonate, and nitrate. The Shenandoah, among 



