MUSSELS OF CUMBEELAND RIVER AND TRIBUTARIES. 59 



In some rivers, as parts of the Illinois, this shell does not become stained early, 

 and the younger shells furnish excellent button material. For the common run of 

 buttons this shell is becoming one of the most important species, as its large size and 

 expanse allows it to be worked up readily into buttons of various sizes, and the stains 

 can be bleached out or the buttons "smoked" or artificially dyed. In the Cumber- 

 land the nacre becomes badly stained, even when the shell is quite small, and the 

 washboards are always sorted out and sold separately as low-grade shells, bringing 

 but .|2 to $5 per ton when first-grade shells are bringing $6 to $8. 



But few parasites were found, and we have as. yet no clue to the cause of the dis- 

 colored spots on the nacre. These spots are usually circular in outline and frequently 

 have what appears to be a foreign body in a small raised pustule at the center. The 

 fresher stains, or those near the surface, do not really permeate the nacre, but are 

 composed of a flat hornlike skin overlying it and can be softened by acids and scraped 

 away from the unstained shell beneath. The older, duller stains are doubtless the 

 same thing covered by layers of nacre. 



Many of our specimens are interesting as showing with unusual clearness the path, 

 during growth, of the posterior adductor muscle scar, the anterior border of which is 

 dimly defined, while straight converging lines from the dorsal and ventral borders 

 of the scar lead up into the umbonal cavity. One of our specimens has a pinkish 

 nacre. 



63. Quadrula cyUndrica (Say) . Rabbit's-foot. 



Occasional to abundant in the upper part of the river. On account of its narrow 

 cylindrical shape it is of little value for buttons; the nacre, moreover, is frequently 

 diseased and stained. The flesh is usually orange yellow and the gills, when filled 

 with glochidia, markedly so. Some of our examples are well covered with small 

 tubercules over the anterior portion of the disk, approacliing the subspecies strigillata. 



This is a rather active species, the most active of the Quadrulas. Its elongate form, 

 in which it differs markedly from its nearest relative, melanevra, and indeed from all 

 Quadrulas in general, may be an adaptation to an active life. 



64. Quadrulametanevra (Rsifinesque). Monkey-face. 



This well-known button species is fairly common. A few were to be found at nearly 

 every station, clam pile, or mussel bed. It was not abundant enough, however, to 

 form more than a sprinkling among the shell piles, and it cuts a rather small figure in 

 the button industry of the Cumberland. On account of its luster and solidity it is 

 very acceptable to the manufacturers. It would not be worth propagating, however, 

 as there are plenty of better species. We found one example of this species gravid on 

 the last of May. 



65. Quadrula tuberosa (Lea). 



Rare and collected only in the upper river. In the autum of 1910 Mr. Boepple 

 obtained it at Sloans Shoals in the South Fork near Burnside, at Selfs Bar, and at 

 Cloyds Landing. 



6G. Quadrula fragosa Com-ad. 



This species is occasional, and in some places abundant, in the lower Cumberland. 

 It does not appear to "bite" readily on the crowfoot hook and the few examples 

 taken by clammers are apparently no indication of its abundance. Small mussels 

 of this species are a favorite food of the muskrat. Of a large pile of shells cleaned 

 out by these rodents near Meeks Spring Bar, nearly all were this species and Ohliquaria 

 rcftcxa, although other mussels appeared to be common in the vicinity. 



This species is very similar to Quadrula lachrymosa (Lea) and the differences between 

 the two are difficult to express either by description or figure. It is somewhat more 

 square-cornered, more inflated, and the tubercles on the posterior slope are more 

 markedly arranged in rows, forming costae. This species does not become as large as 



