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 thé 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 is, 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-Back; 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 
