FRESH-WATER MUSSELS. 103 



Baker (1918, p. 117) gives a summary of results of studies of mussels with reference 

 to bottom and depth in Oneida Lake, N. Y., in the following words: 



The greatest number of individuals occurred on a clay or sandy-clay bottom. Twice as many 

 mussels occurred in water deeper than 6 feet than within the 6-foot contour. These features are 

 expressed in Table No. 27, the figures being averages per unit area of 9 square feet. 



Table No. 27, — Aver.-^ge Number of Mussels on Botto.m, 



Bowlder and gravel bottom 6. 14 



Sand 6. 39 



Clay and sandy clay 13- 00 



Mud 10. 26 



Within 6-foot contour 7. 84 



Outside 6-foot contour 16. 85 



The above table shows that mussels are more abiuidant on the mud bottom in deep water (8 to 14 

 feet) than on sand, gravel, bowlder, or clay in shallow water (i to 6 feet). These are the only studies of 

 this character known to me. 



In that lake one species, Anodonta implicata, is reported from one kind of bottom 

 only, in sand between bowlders; while another species, Lampsilis luteola Lamarck, is 

 said to be common on all varieties of bottom, except gravel (Baker, 1918, pp. 161, 162). 



Muttkowski (191 8) found that sand bottoms marked the favored environments 

 of fresh-water mussels in Lake Mendota, Wis. 



In Lake Pepin most of the adult mussels are found on a bottom of gravel or a 

 mixture of gravel and sand. Bottoms composed largely of mud but made firm by a 

 mixture of sand or gravel or both, yield a good supply of mussels; such areas are of 

 much less extent in the lake than bottoms of gravel or gravel and sand. Of 1,397 

 juvenile mussels comprising 16 species collected in Lake Pepin in 1914, practically 95 per 

 cent were taken on a sand bottom; about 4 per cent, principally Anodonta inibecillis, 

 were found on a mud bottom ; and the remaining i per cent on gravel or a mixture of 

 sand, gravel, and mud (Shira, report in manuscript). 



In ponds and sloughs there is less choice of bottoms than in lakes, and mud bot- 

 toms usually prevail; for such conditions Lampsilis parva, LampsUis subrostrata, the 

 light-shelled Anodontas, and similar species are especially adapted. 



When we consider the relation between various mussel species and the bottom in 

 rivers, we find the matter complicated by several considerations. This much, however, 

 may be said definitely: No mussels can survive in a shifting bottom, nor upon a bottom 

 of solid bare rock. Between the extremes, beginning with clean sand or soft miry silt 

 and ending with coarse gravel and bowlders or stiff clay, there is a great variety of 

 bottoms utilized to a greater or less extent as habitats for various species of mussels. 



There are, of course, more or less definite relations between bottom and other 

 features. Soft, muddy bottom is always associated with a current that is feeble at 

 least near the bottom, or vnth the checking of the current; gravel bottom is usually 

 associated with swift current; and clean sand or gravel is associated with clear water. 

 Certain of the "mud-loving" mussels, such as the Anodontas, may be really lovers of 

 quiet places and their association with mud rather an accident. Some of those supposed 

 to be partial to sandy or gravelly bottom may simply prefer clear to turbid water, or 

 mav thrive best in a swift current. 



