32 ILLINOIS BIOLOGICAL MONOGRAPHS [130 



nor is it listed by other students. It has been reported by several concholo- 

 gists from the Wabash River (Baker, 1906:79) and the Ohio River, in which 

 streams it is common and of large size and fine color. The species probably 

 would not thrive in polluted water. It was not found in the Sangamon 

 River at the places visited. Owing to its peculiar shape it is not adapted 

 for the cutting of button blanks and is considered worthless by the mussel 

 fishermen. 



2. Quadrula (Quadrula) metanevra Rafinesque. Monkey-Face. 



This naiad is apparently a rare species in Salt Fork occurring sparingly 

 from Homer Park to Middle Fork. It begins to increase in number of 

 individuals near the Middle Fork, where the specimens are also larger 

 and more brilliantly colored. All but one of the specimens collected are 

 typical in form and coloring. Individuals from the Big Vermilion below 

 Middle Fork are larger than those collected above this point. The species 

 is also more abundant. It is found on both a mud and a gravel-sand bot- 

 tom. Specimens from Homer Park are darker and less conspicuously rayed 

 than those from Middle Fork, and are also less pustulose. Metanevra is 

 rare in the Sangamon River, living on both a sand and gravel bottom. 



2a. Quadrula (Quadrula) metanevra wardii (Lea). 



Two specimens referable to this variety have been collected from the 

 Big Vermilion; one near Muncie, in the Salt Fork, and one in the Middle 

 Fork, above its entrance into the Vermilion River. These individuals 

 are more elongated and compressed than the typical form and the tubercles 

 are not as heavy, in fact are reduced to large pustules. Professor Smith 

 has found the variety more common in the Sangamon River than the 

 typical form, and until these two specimens were found in the Big Vermilion 

 drainage, wardii was supposed to be the predominant form in the Sanga- 

 mon while the typical form was believed to be the only form of this species 

 found in the Big Vermilion, at least above Danville. Wardii i^, as far as 

 present material indicates, very rare in the Salt Fork and other tributaries 

 of the Big Vermilion. 



3. Quadrula (Theliderma) pustulosa (Lea). Warty-^&ack; Pimple-Back. 



This is the most abundant Quadrula in both the Salt Fork and the San- 

 gamon River, rivalling in number any other mussel species in the lower 

 part of the Salt Fork. It does not occur in any abundance above the 

 Homer Park dam, but below this point it is common, of large size, fine 

 color, and good nacre. The sewage pollution has evidently affected this 

 species as others and, with rare exceptions, only dead shells could be found 

 above the Homer Park dam. Below the dam it occurs commonly and the 

 increase in number of individuals is largely due to the aerating effect of 

 the flow of water over the dam which provides the dissolved oxygen so 



