FRESH-WATER MUSSELS AND MUSSEL INDUSTRIES. 25 



of Q. ebenus, its commercial value is not of first rank ; the shell can not be worked up as 

 economically as that of some other species and is usually cut into small-sized buttons. 

 The pig-toe (formerly called Quadrula trigona) is a summer breeder. 



Ohio River pig-toe, Quadrula ohliqua (Lamarck) (PI. VIII), is the commonest mussel 

 in the Ohio River. It is found throughout its entire length as far as mussel beds extend. 

 It often forms 80 per cent of the mussels in a bed. In some places in the Cumberland 

 River this is the most common mussel, and the shells from the Cumberland River are 

 superior to those of the Ohio. It is found also in the Illinois River, but is rarely, if ever, 

 seen in the Mississippi. 



The commercial value of its shell is not high. When first marketed from the Ohio 

 River it brought only $1 to $2 per ton, and buyers were difficult to obtain at that price. 

 In 1910 the price reached $8 per ton, but it has been higher since ($12 to $13 in 1914, 

 and about $30 in 191 9). The material has a poor luster and is chalky, and only the 

 butt part of the shell can be used, as the iridescent portion of the shell is too thin. The 

 nacre is often marked with green spots, and many shells are eroded at the umbones, 

 these qualities being more evident in the shells from the upper portion of the river. 



Qvxidrula plena (Lea) (Pi. VII) and Quadrula pyramidata (Lea) (PI. XII) are two 

 species that are distinguished taxonomically, but they can not be differentiated com- 

 mercially from the other pig-toes. 



The flat niggerhead, Quadrula coccinea (Conrad) (PI. IX) and the Wabash pig-toe, 

 Qu^rula ruhiginosa (Lea) (PL IX), are found principally in the small rivers. Both 

 species are reported from the Grand River, Mich., and coccinea is common in the James 

 River, S. Dak. They are not uncommon in the small outlets of lakes of the northern 

 States. While the extreme forms are readily recognized, the two species run into each 

 other (in external appearance), so that they are often confused. Ruhiginosa has a pro- 

 nounced posterior ridge. In shape the shells are sometimes rather circular (as is especially 

 true of coccinea) or rhomboidal. They are more compressed than the ordinary run of 

 niggerheads or pig- toes and have a relatively light-colored epidermis. The shells are 

 somewhat puzzling to fishermen but are often called flat niggerheads or thin nigger- 

 heads. They are not, however, closely related to the niggerheads in scientific characters 

 or commercial qualities. 



Mr. Southall states that the nacre is sometimes rather soft, like the pig-toe, and 

 sometimes very hard, like the bullhead {Pleurobema cesopus). It so happens that coccinea 

 (but not ruhiginosa) is placed by Dr. Ortmann in the genus Pleurohema. It is probable, 

 therefore, that the commercial qualities, as well as the scientific positions of the two 

 species, are quite distinct; but, in the lack of final information and with the present 

 confusion in common parlance, they are mentioned together. The nacre of both species 

 is of fair quality, but the iridescent part is too thin to be used. Coccinea often has a 

 pink nacre, and in this case it is sometimes called "pink niggerhead." 



The spawning times of both species are probably early summer and midsummer. 



BLUE-POINT GROUP. 



We come now to species that are much larger in size, always with rough, ridged backs 

 and with a quality of nacre somewhat inferior to the shells of the niggerhead. Many of 

 them are well esteemed, especially because so many blanks can be cut from the single 

 shell, and because they are adapted for the larger sizes of buttons. 



