YE MT me, ey 
PAPERS ON ZOOLOGY 161 
Subgenus Lasmigona s. s. 
20. L. costata (Rafinesque)—White Heath and Monticello 
only. This also is a deep river species which ascends in small 
numbers such tributaries as the Sangamon. It prefers muddy 
bottoms, but at one station it was the only form among the 
rocks. Muskrats prefer this species to other clams. This may 
account for the non-abundance of costata in shallow waters. 
Subgenus Pterosygna Rafinesque, 1851 
21. L. complanata (Barnes)—White Heath and Monticello, 
Piatt Co., St. Joseph, Champaign Co. Its habitat is much the 
same as that of L. costata and the two are usually found to- 
gether. Amblema undulata is also usually associated with 
them. <A specimen of complanata was found which measured 
ten inches across. Young shells are plentiful, and in many in- 
stances are distorted by cow hoofs. 
GENUS ALASMIDONTA Say, 1818 
Subgenus Pressodonta Simpson, 1900 
22. A. calceola (Lea)—White Heath and Monticello. As- 
' sociated with A. marginata, on muddy bottoms in water only 
a few feet deep. 
Subgenus Rugifera Simpson, 1900 
23. A. marginata (Say)—White Heath, Monticello and Hil- 
lery. With the preceding species; not very abundant. 
GENUS ELLIPTIO Rafinesque, 1819 
Subgenus Elliptio s. s. 
24. HE. gibbosus (Barnes)—White Heath, Piatt Co., col- 
lected by Dr. Charles C. Adams; also at Hillery, Vermilion 
Co. It prefers flowing waters of a few feet in depth only, with 
muddy bottoms in which these clams usually remain buried. 
GENUS UNIOMERUS Conrad, 1853 
25. U. tetralasmus (Say)—Crystal Lake, Champaign Co. 
Found always buried deeply in mud of quiet waters. 
GENUS PLEUROBEMA (Rafinesque, 1820) Agassiz 
26. P. clava (Lamarck)—Hillery, Vermilion Co., Dr. J. D. 
Hood, collector. This is another of the typical members of the 
Wabash River drainage. It prefers deeper waters, usually 
muddy bottoms. 
