48 ILLINOIS BIOLOGICAL MONOGRAPHS {146 
24. Amygdalonaias elegans (Lea). Deer-Toe. 
But one specimen of this peculiar species was found. This individual 
was collected by Professor Smith at the big bend below the natural dam. 
The specimen was an empty shell, iron stained outside and inside, and 
apparently had not been living for a considerable time. It is typical in 
form but not as large as individuals from the larger rivers. The measure- 
ments of this specimen are: length, 57; height, 47; width, 27 mm. That 
but one specimen of this species should have been collected in this river 
drainage seems quite surprising, indicating, probably, that the species 
has not been able to become established. It is not found in the Sangamon 
River as far as known. 
25. Obovaria circulus (Lea). 
This nearly circular mussel was collected at but five stations in the 
Big Vermilion River; Homer Park below the dam, near Muncie, Salt Fork 
near Middle Fork, in Middle Fork, and in the Big Vermilion below Middle 
Fork. It is infrequent at the first place and abundant only in Middle Fork, 
near its junction with Salt Fork, on a gravel and sand bottom, in fairly 
shallow water (September) and in the Big Vermilion (October). In the 
Big Vermilion this species is very uniform in shape and size, the ratios of 
height to length ranging between 70 and 90 percent. The shells are usually 
nearly circular and have a distinct light yellowish-brown zone at the pos- 
terior margin. The nacre is pearly and there are no evidences of discolora- 
tion from injury or parasitism. It has not been found in the Sangamon 
River. 
As in the case of so many of our mussels whose names have become 
familiar, this species may have to be changed to that of subrotunda Rafin- 
esque (1820). 
26. Actinonaias ligamentina (Lamarck). Mucket. 
This mussel was not found above the Homer Park dam. It occurred 
infrequently (almost rarely) below the dam on both a mud and a gravel 
bottom. In the Salt Fork near its junction with Middle Fork but one dead 
shell was found in half a days search for a distance of nearly a mile up 
stream. In Middle Fork, between the interurban bridge and the mouth 
of the stream, it was fairly common on a gravel and fine sand bottom in 
shallow water near riffles. In the Big Vermilion below Middle Fork it is 
the most abundant mussel, attaining a length of over 135 mm. 
The individuals of this species are all normal specimens; the young and 
half-grown shells are greenish with many dark green rays of various width. 
Older shells are yellowish with few rays. In an old shell measuring 120 mm. 
in length and 75 mm. in height the rays showed but faintly (Z 11216). 
Evidences of distomid enfection were rare in this species in the Big Ver- 
