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PAPERS ON ZOOLOGY 163 
current is sluggish or wanting. Usually associated with Muscu- 
lium transversum. This Sphxrium was often found in places 
completely dried up in the Summer. 
30. NS. sulcatum (Lamarck)—In soft mud at Crystal Lake, 
near Urbana. Not abundant. 
36. S. solidulum Prime—A form very close to this species, 
and probably referable to it, was collected in mud at Crystal 
Lake, near Urbana; rare. 
37. WS. stamineum Conrad—Monticello, Piatt Co., St. Joseph 
and Homer Park, Champaign Co. In small creeks, rivers and 
ponds, buried in mud or among the roofs of aquatic plants. 
38. S. striatinwm Lamarck—Very abundant at Crystal 
Lake, St. Joseph, and the Salt Fork, Champaign Co., and at 
Hillery, Vermilion Co. It lives in soft mud, or at times sandy 
situations, buried often to a depth of eight inches. Among 
roots of water plants, associated with Musculium transversum 
and M. partumeium. 
GENUS MUSCULIUM Link, 1807 
39. M. partumeium Say—Crystal Lake, Salt Fork and 
Urbana, Champaign Co. Not very abundant, associated with 
transversum in soft, muddy bottoms. 
40. M. transversum Say—Very abundant in all three coun- 
ties, perhaps the most abundant of all the Spheriide. Gregar- 
ious, usually associated with M. partumeium, NS. striatinum, 8. 
occidentale and some species of Pisidia. It lives in soft mud in 
ponds and slowly moving streams, under and among stones, 
among roots of aquatic plants and similar situations. Individ- 
uals were found with from 20 to 30 young within the mantle 
cavity. 
41. M. truncatum Linsley—Reported from Urbana by Dr. 
Frank C. Baker, the specimens being in the collections of the 
Ill. State Lab. Nat. Hist. 
GENUS PISIDIUM Pfeiffer, 182 
42. P. compressum Prime—Crystal Lake and Salt Fork, 
Champaign Co., buried in soft mud or among the roots of 
aquatic plants. It was very abundant in small streams and 
lakes. 
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