The Pearly Fresh-water Mussels 



with single lateral in right valve, two in left; female shell swollen 

 in posterior ventral region to accommodate marsupia, which 

 occupy the hinder part of outer gills; mantle margins doubled 

 -and thickened. 



L. ventricosus, Barnes, with a thin, inflated shell, is the 

 "pocket-book" clam of the button factories. It is the type 

 species of the genus. Its range includes the drainage of the 

 St. Lawrence and Mississippi rivers. ' 



L. capax, Green, is another "pocket-book," obtained from 

 the lower Ohio River drainage, north to eastern Iowa, south- 

 west into Arkansas. It is locally abundant. 



L. alatus, Say, has a strong dorsal wing set off by a ridge 

 that runs backward from the beaks. It is a large species, with 

 dark, cloth-like epidermis, and purple nacre. It inhabits the 

 St. Lawrence and Mississippi river systems, and the Red River 

 of the North. It reaches the Arkansas River. 



L. ligamentinus, Lam., is the "Mouquet," "Mougat," or 

 "Mucket," a fine button shell with silvery, sometimes pinkish, 

 pearl lining. 



L. anodontoides, Lea, is a solid, inflated shell, pointed be- 

 hind, with a shiny yellow epidermis and lustrous white or purple 

 nacre. It is the "yellow-back" or "yellow sand shell" used 

 for buttons. It is found throughout the Mississippi and Gulf 

 drainage. 



Genus TRITIGONIA, Agassiz 



Shell solid, elongately rhombic, with strong, irregular pos- 

 terior ridge, obliquely truncated behind in the male shell, com- 

 pressed and rounded in the female; surface covered with pustules. 



T. tuberculata, Barnes, is the "deer-horn" or "buck-horn," 

 the largest species that furnishes material for pearl buttons. The 

 average "niggerhead," three or four inches long, cuts four or five 

 "blanks" — disks that are ground down into buttons. A large 

 deerhorn will cut four times as many, though not proportion- 

 ately larger. 



Habitat — Mississippi drainage and streams flowing to the 

 Gulf from the Alabama River to Central Texas. 



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