FRESH-WATER MUSSELS. 



107 



recoided (by one observer) as finding the most favorable en\'ironment in a bottom of 

 clay unmixed with sand. 



Table 6 may be simplified by reducing the types of bottom to four general classes, 

 sand, gravel, mud, and clay, and by eliminating all but the leading commercial species. 

 The results are indicated in Table 7 following: 



Table 7. — Preferred Habitats op Leading Economic Fresh-water Mussels, According to 



Character of Bottom. 



[X indicates preference as noted by majority and x by minority of observers.] 



Scientific name. 



Common name. 



GraTel.l' 



Mud.' 



Clay.* 



Lampsilis anodontoides 



Lampsilis fallaciosa 



Lampsilis recta 



Lampsilis ligamentina 



Lampsilis ligamentina gibba. 



Lampsilis luteola 



Lampsilis ventricosa 



Obovaria ellipsis 



Plagiola securis 



Quadrula coccinca 



Quadrula ebenus 



Quad rula heros 



Quadrula Jachrymosa 



Quadrula metanevra 



Quadrula obliqua 



Quadrula plicata 



Quadrula pustulosa 



Quadrula rubiginosa 



Quadrula undata 



Quadrula undulata 



Unio crassidens 



Unio gibbosus 



Yellow sand-shell . . 

 Slough sand-shell . . 

 Black sand-shell . . . 



Mucket 



Southern mucket. . 



Fat mucket 



Pocketbook 



Hickor>-nut 



Butterfly 



Flat niggerhead . . . . 



Kiggerhead 



\Va,shboard 



Maple-leaf 



Monkey-face 



Ohio River pig-toe. 



Blue- point 



Pimple-back 



Pig-toe 



Three-ridge . . . . 

 Elephant's ear. 

 Lady-finger. . . 



X 

 X 

 X 



X 



X 

 X 



X 

 X 



X 



X 



x' 



X 



x 



X 

 X 



X 

 X 



X 

 X 



a Sand alone. 



b Including sand and gravel, mud and gravel, and rocks. 



c Mud alone. 



* Including sand and clay, mud and clay. 



DEPTH. 



The distribution of many animais of the water is know-n to be influenced by depth, 

 theeffect of which may be felt, among other ways, through pressure, light, temperature, 

 dissolved gases, and freedom from wave action, or exposure thereto. In an indirect way, 

 too, the effect of depth is experienced by any animal through the influence of these 

 conditions upon food and enemies. 



The increase of pressure is approximately i atmosphere for each 10 meters (33 

 feet) in depth, but fresh-water mussels are, so far as knov\-n, restricted to shallow waters 

 where pressures must be insignificant. The Spha:riids are the only mollusks found 

 below the 25-meter line in Lake Michigan (Shelford, 1913). Maury (1916, p. 32), (see 

 Baker, 1918, p. 155), reporting the results of dredging in Cayuga Lake, N. Y., says: 

 "These dredgings proved conclusivelj' that Mollusca after 25 feet become very scarce. 

 * * * In the greater depths no signs of Mollusca or of plants were found." In 

 clear water minor depths do not markedly affect the light, but if the water is turbid, a 

 common condition in the environment of fresh-water mussels, the penetration of light 

 is very much diminished (see p. 114), and mussels if affected by light may, therefore, 

 be expected to live at greater depths in clear lakes than in turbid streams. Temperature 

 changes due to depth alone are so inconsiderable for shallow water as doubtless to have 

 little effect upon the distribution of mussels, except where freezing to the bottom may 

 occur. 



