58 ILLINOIS BIOLOGICAL MONOGRAPHS [156 
and Wabash rivers. The small size of the Danville specimens may be 
due to the fact of their inhabiting the upper part of their distributional 
range, in a rather small river. Rafinesque’s name torulosa has been 
used by Conrad, Agassiz, Reeve, and Ortmann for Truncilla perplexa 
and if the original description is clear enough to reasonably fix the shell 
as Lea’s perplexa this form will stand as Truncilla torulosa rangiana 
(Lea). Neither perplexa or rangiana are known from the Sangamon River. 
FAMILY SPHAERIIDAE 
37. Sphaerium striatinum (Lamarck). Variety. 
This finger-nail clam occurs abundantly only in the ditch north of 
Urbana. It also occurred infrequently in Spoon River, and near the 
iron bridge in Salt Fork north of Sidney. Dead specimens were 
found at bench mark 655 and below the Homer Park dam. 
Sterki remarks of this form “possibly a form of striatinum Lam; 
apparently the same as a Sphaerium from Iowa and other places which for 
many years has been left unnamed, except in manuscript. It still seems 
impossible to say where the limits of striatinum are.’ The writer fully 
agrees with Dr. Sterki regarding the variation in this common species. 
This variety appears quite distinct from the ordinary specimens of the 
species and it is to be hoped that Dr. Sterki will give it a name. It is 
noteworthy that the form occurs commonly only in the drainage ditch above 
Urbana and was not found in any numbers below this place. A Sphaerium 
identified as striatinum by Zetek some years ago, occurring in Crystal Lake, 
was doubtless this form. 
38. Sphaerium stamineum (Conrad). 
This small mussel is abundant at several places in Salt Fork above 
Sidney. It occurs only infrequently at two other places. Reported by 
Zetek from Crystal Lake. Some of the shells are typical but others are 
similar to straitinum and it is difficult to separate some specimens from that 
species. At the station called bench mark 655 a form of this species 
occurs that is somewhat like the variety forbest Baker, described from 
Mason County, Illinois. 
39. Sphaerium solidulum (Prime). 
An abundant species in the Spoon River and in the Salt Fork above 
Sidney. Occurs rarely at other places. Reported by Zetek from Crystal] 
Lake. On the whole this species is quite uniform in characters. 
40. Sphaerium species. 
A Sphaerium occurs abundantly in Salt Fork below the Homer Park 
dam which is thought by Sterki to be possibly a new species. It is related to 
solidulum but is larger and more robust (mus. no. Z11383). It lives in 
