26 BUIylyETlN OF THE BUREAU OF FISHERIES. 



The species are not so restricted in parasitism as the niggerhead and the pimple- 

 backs, and plicata, at least, is carried by several of the game fishes. 



The blue-point, Quadrula plicata (Say) (PI. X), and the three-ridge, Quadrula undu- 

 lata (Barnes) (PI. X), two very similar mussels, called by the mussel fishermen blue-point 

 and three-ridge, are among the most widely distributed species in the whole Mississippi 

 Basin, being found in most of the rivers and larger creeks in different sizes and forms. 

 Plicata is the thicker species, with heavier umbones, common in the deeper and more 

 sluggish waters, while undulata is flattish and characteristic of headwater or tributary 

 streams. The species seem to intergrade, so that it is frequently difficult or impossible 

 to distinguish them. The clammers do not seem to recognize the two species, but apply 

 the term three-ridge or blue-point indiscriminately. 



Generally speaking, these mussels, even when clear of spots, work with a good deal 

 of waste, on account of the heavy hinge and teeth, and they yield a considerable number 

 of second and third grade buttons, although some buttons of very good quality are also 

 produced, including a few iridescents. Blue-points, three-ridges, and washboards (see 

 below) were worth about $12 per ton in 1914, and about $30 in 19 19. 



The commercial value of the shells varies greatly in different rivers and creeks. 

 In the Mississippi River, for example, the young mussels can be sold with the nigger- 

 heads. The value of the shell decreases as the mussel grows older. The shell loses 

 iridescence and becomes more brittle and hard, and consequently difficult to work up; 

 the layers lose their firmness of attachment, so that they split off easily. Old shells, 

 moreover, are frequently spotted. It is found in manufacture that the iridescence of 

 tips from these shells is enhanced by the processes of bleaching. These mussels spawn 

 in midsummer. 



In the streams of the gulf drainage in Florida, Georgia, and westward these species 

 are replaced by Quadrula per plicata (Conrad), Quadrula elliotti (Lea), and Quadrula 

 neislerii (Lea). Quadrula perplicata occurs in the Cumberland under the common 

 name of round-lake shell. 



WASHBOARD GROUP. 



This group comprises, practically speaking, only a single species. 



The washboard, Quadrula heros (Say) (PI. XI), is the largest and heaviest species 

 of mussel in the Mississippi Basin. One example 8 inches wide and 1 1 inches long and 

 weighing over 4 pounds with the flesh, was collected by the late J. F Boepple in the 

 Salt River, Ky. The empty shell weighed about 3K pounds. 



The washboard is found chiefly in large rivers in quiet, deep water and on gravel 

 and mud bottoms. 



The Wabash and Illinois Rivers have the highest percentages of washboard, although 

 there are beds in the Ohio River where this species forms nearly 50 per cent of the catch. 

 The shell is generally of an oval outline and more or less elongated. It is valued chiefly 

 because of its large size, making it suitable for cutting the largest-sized buttons. The 

 material is tough and the grain uniform and regular. The iridescent part breaks easily 

 in sawing, owing to the undulations on the back. The nacre is usually discolored with 

 yellowish or greenish spots, and the older the shell the larger are the spots. We have 

 received pink shells from the Illinois River. Young mussels from 3 to 4 inches long have 

 only a few spots or none, and the iridescent part is as thick as in the older mussels, 

 being thick enough for buttons. This part of the washboard is very similar to the 



