I04 



BULLETIN OF THE BUREAU OF FISHERIES. 



Several species, including most of the Anodontas, Symphynota complanata, Arcidens 

 confragosus, and others, are confined chiefly to one sort of bottom. A great many, 

 however, seem indifferent to the character of the bottom, provided other conditions are 

 favorable. Mussels may also apparently thrive where one would naturally think condi- 

 tions unfavorable and where they might not survive if artificially planted. Thus in the 

 crescent-shaped bayous along the Kankakee Quadrula undulata, and in sloughs of the 

 Mississippi a closely related mussel, both heavy-shelled species, are found thriving on the 

 top of deep, soft, silty mud which would not seem stiff enough to bear their weight. 



In the Grand River, Mich., various species of mussels were found upon "clean" 

 sand bottoms, but always sparsely. Quadrula undulata and Lampsilis ellipsiformis and 

 ventricosa seemed best adapted to life in accumulations of drift. In sewage and waste- 

 polluted waters at Lansing, Mich., Lampsilis ligamentina, venlricosa, and ellipsiformis, 

 Quadrula coccinea, Symphynota costata, and Alasmidonta marginata were found in appar- 

 ently healthy condition. The Lampsilis ellipsiformis obtained there, of especially large 

 size, bore innumerable (but worthless) small pearls. (Coker, unpublished notes.) 



In the Mississippi River near Fairport, Iowa, bottoms of unmixed mud and pure 

 sand were found to be much less occupied by many of the species than mixtures of gravel 

 and sand or of sand and mud, which supported both a far greater number of individuals 

 and a somewhat greater variety of species. The preference for certain bottoms is most 

 conspicuous when the proportion of the total catch of mussels found on the favored 

 bottoms is ^dewed in connection with the proportions of these bottoms in the total area 

 sur\'eyed. Table 5 shows the total number of mussels taken from the different types of 

 bottom in a survey of Andalusia Chute, Mississippi River (Howard, report in preparation) : 



Table 5. — Mussels Collected in Survey op Andalusia Chute, with Reference to Character 



OP Bottom. 



Composition of bottom. 



Approxi- 

 mate per- 

 centage o( 

 total area 

 of bottom. 



Number of 

 mussels. 



Number of 

 species. 



Mud 



Mud and sand 



Mud and ledge rock 



Sand 



Sand and gravel 



Sand and pebbles 



Gravel ( pure) 



Gravel, cobbles, and rock 



Gravel and mud 



Pebbles 



Rock 



71 

 9 



44 



158 

 17 

 87 



289 



29 



S 



34 



7 

 a3 

 28 

 12 



3 

 M 



The niggerhead mussel, Quadrula ebenus, in some streams, at least, is said to show a 

 decided preference for firm bottoms, as of gravel or blue clay, but few observations have 

 yet been made upon these mussels in streams having considerable areas of clay bottom. 

 In the Grand River, Mich., the pink heel-splitter, Lampsilis alata, was found lixang in a 

 ledge of very tough slippery blue clay (Coker, unpublished notes). So finn was the clay 

 that a mussel could be extricated from it only by the exertion of considerable muscular 

 efifort. Several other species of mussel were in the vicinity, but none were embedded in 



