no BULLETIN OF THE BUREAU OF FISHERIES. 



factors are favorable. In various parts of the country considerable commercial quan- 

 tities of mussels are collected by hand from shallow waters. At one such place, Lyons, 

 Mich. , the mucket, Lampsilis ligamentina comprised 80 per cent of the collection, although 

 the three-ridge, Quadrula undulata, the pocketbook, Lampsilis ventricosa, the spike, 

 Unio gibbosus, and the black sand-shell, Lampsilis recta, were quite common. Among 

 other species that were frequently found in very shallow water (i to 2 feet in depth) in 

 that stream were the following: Lampsilis luteola, iris, and ellipsiformis, Quadrula 

 coccinea and rubiginosa, Strophitus edentiilus, Symphynola compressa and costata, Alasmi- 

 donta marginata, Anodontoides jerussacianus, and Anodonia grandis. In fact, the only 

 species that were not found in water less than 6 feet in depth in the Grand River were 

 the three-homed warty-back, Obliquaria reflexa, the hickory-nut, Obovaria ellipsis, the 

 deer-toe, Plagiola elegans, and the white heel-splitter, Symphynola complanata. 



LIGHT. 



The small floater, Anodonta imbecillis Say, in sunlight will draw in its siphons when 

 ashadow passes over. Wenrick (1916) has demonstrated experimentally with measured 

 Illumination, that a fresh-water mussel, Anodonta cataracta ,Say, is very sensitive to 

 decrease in intensity of light. Observations in the Washington laboratory indicate that 

 the yellow sand-shell, Lampsilif anodontoides, will close when a black cloth is placed 

 over the aquarium, but will open when exposed either to daylight or to the light of a 

 bright electric lamp. These reactions may be for protection of the animal from approach- 

 ing enemies, but it is probable also that the distribution of mussels is largely influenced 

 by light conditions. Mussels are seldom found in vegetation which is dense enough to 

 exclude the light to a great extent. This is especially true with regard to plants like the 

 water lily which have floating leaves. Some relations to vegetation are brought out 

 in a study of the habitats in Oneida Lake (Baker, 191 6). 



An exceptional case is reported by Wilson and Danglade (1914, p. 15) where the 

 mussels were found in densest aggregation submerged deeply in the bottom and below 

 a covering of vegetation. Their account is of sufficient interest to be quoted in full : 



The bottom of the river where these shells are obtained is covered with algae and water weeds to the 

 depth of 12 to 18 inches, and the thicker the vegetation the more plentiful the mussels beneath it. Two 

 men were actively working the Shell River at Twin Lakes near Menahga at the time of our visit, and we 

 watched them rake off the algae and weeds and then dig into the underlying gravel and sand for the 

 mussels. The latter are often buried to the depth of a foot or more. This is, at the least, a novel con- 

 dition and one which, so far as is known, has not been reported from any other locality. 



Certain species of mussels, the mucket, pocketbook, black sand-shell, and others 

 are sometimes pink-nacred and sometimes white-nacred, and with the two former, at 

 least, the outside covering of the shell has a reddish cast in pink-nacred examples. 

 With such species it is a matter of common observation that pink-nacred shells and 

 brightly colored exteriors are more frequently found in shallow clear water where the 

 mussels are exposed to bright light." Thus the black sand-shells of the upper part of the 

 Grand River, Mich., have a deep purple nacre, while white shells of the same species 

 predominate in the more turbid Mississippi. The spike, Unio gibbosus, is usually purple- 

 nacred, but uncommon examples that are nearly white are found in turbid rivers. Clark 



a Grier (1920a) presents the result of aa extensive study of the nacreous color of mussels. He notes a tendency to lighter or 

 bluish nacreous color in the lower portion of stream courses- He has evidence of some correlation between color and sex. 



