Quarterly Journal of Co)ichology. 389' 



appears to me our pond Melanfko is called by some, decisa. 

 It is lighter, more pointed, and whirls not so much shoul- 

 dered as the river form. 



LiOPLAX SUBCARINATA, Say. Common in ponds; some shells are 

 not carinated and can scarcely be separated from the pond 

 Melantho. Typical specimens are bluish horn color and 

 strongly carinated. 



Rissoidae. 



Bythinella obtusa, Lea. Rare; in a few ponds in^YOods; shells 



all apparently truncated. 

 SoMx\TOGYRUS isoGONUS. Say. Common in i)onds or sluggish 



streams. 

 Amnicola porata, Say. Common with 6". isogonus. 



A. ciNCiNNATiENSis, Authony. Abundant with porata, and in 

 some ponds where the latter does not occur. 



Strepomatidae. 



Pleurocera sueulare, Lea. Abundant in lower end of Burdett's 

 Slough at time of low water last summer; previously I had 

 found but a few dead shells alono; the river shore. 



Unionidae. 



Anodonta corpulenta, Cooper. Common in our sloughs and 

 Keokuk Lake. Rather tumid, short, lower margin quite 

 convex. This species somewhat resembles grai/dis into 

 which I believe it varies. 



A. GRANDis, Say. Abundant in Keokuk Lake. Shell longer, 

 straighter on lower margin, less tumid than the typical 

 corpulenta. The young of these two species seem to be 

 much more readily separated than the mature shells. 



