MUSSEL S-AUNA OF THE KANKAKEE BASIN. 41 



Viewed in this light, Q. tuherculata is not altogether unimportant 

 as a commercial species. Its shell is the package that may contain 

 a prize — usually a worthless trinket, but always arousing expectancy. 

 Q. tuherculata adds more markedly than any other species to the 

 size, but hardly to the value, of the clammer's pile of slugs or 

 " chicken feed " which furnishes, in some cases a small, in others a 

 considerable addition to the revenue derived from the sale of his 

 shells, and it is indeed one of the strongest incentives to persistence 

 in the clammer's trade, as it furnishes not so much in actual cash as 

 the element of luck or chance, and keeps him in constant expectancy 

 of a possible great discovery. 



Accordingly, it is not improbable that clamming operations the 

 country over depend in no inconsiderable degree on the presence 

 of this and similar species, not directly useful of themselves, but 

 appealing to the instincts of the treasure seeker, the nomad, and 

 adventurer, who can not endure the monotony of a steady, uneventful 

 trade and who require some special incentive or stimulus to 

 persistency. 



This species is of value as furnishing in almost any part of the 

 countiy readily available material for the study of the natural causes 

 and phenomena of pearl production and will probably prove in the 

 end one of the gateways through which our knowledge in that direc- 

 tion, and its practical applications, will come. 



We did not find this species in the headwat^.rs of the Kankakee 

 or Yellow Rivers, though it is common in the Tippecanoe, not far 

 distant. The first found in the Kankakee was at Momence, 111., and 

 in the lower stretches of the river. It was also found in the Iroquois. 



The systematic position of this species is doubtful. We have never 

 found it gravid, and it is, apparently, but rarely found in that condi- 

 tion. It is reported to bear glochidia in only the outer gills. When 

 ground and polished for ornament, this is one of the most attractive 

 of shells. 



^. Quadrula ehena {Lea). Niggerhead. — This, the most valuable 

 of button shells, does not occur within the Kankakee Basin, though it 

 is fairly common in parts of the Illinois River, below. We found one 

 specimen of what appeared to be this shell at Tippecanoe Lake, where 

 its occurrence is difficult to account for. 



3. Quadnila coccliwa {Conrad). — Q. coccinea is, at its best, a 

 very good, if not excellent, button shell. The assemblage of forms 

 that pass under this name exhibit so much variation, however, that 

 no general statement can be made concerning it. It has no trade 

 name, probably because it has not been found in great quantities in 

 regions exploited by the button industry and partly because of its 

 lack of distinctive characters. But it is found throughout the length 

 of the Kankakee and Yellow River systems wherever shells thrive 

 at all, being represented by specimens in 22 of the 35 river stations 



