26 BULLETIN 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) (Pl. X), and the three-ridge, Quadrula wndu- 
lata (Barnes) (Pl. 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 1919. 
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 perplicata (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) (Pl. XI), is the largest and heaviest species 
of mussel in the Mississippi Basin. One example 8 inches wide and 11 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 314 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 
