viii List of Figures. 



Arcidens confragosus (Say). Male from Bayou Pierre, De Soto Parish, 



Louisiana 285 



Left gill of sterile female from Pearl River, Hinds County, Mississippi . 285 



Anodonla cygnea (Linnaeus). Male from Obra South Canal, Sepno, Posen, 



Germany 287 



Left gills of sterile female from Mogelnitza River, Province Posen, 



Germany 287 



Anodonla complanata Rossmaessler. Male from Woernitz River, Dinkels- 



buhl, Bavaria 288 



Left gills of sterile female from same locality 289 



Ptychobranchus sublentus (Say). Gravid female from Cumberland River, 



Pulaski County, Kentucky 308 



Obliquaria reflexa Rafinesque. Gravid female from Bayou Pierre, De 



Soto Parish, Louisiana 310 



Cy progenia irrorala (Lea). Gravid female from Ohio River, Scioto 



County, Ohio 313 



Dromus dromas (Lea). Gravid female from Cumberland River, Cumber- 

 land County, Kentucky 315 



Gravid female of same species from Cumberland River, Wayne County, 



Kentucky 316 



Left gills of gravid female of same species from Cumberland River, 



Russell County, Kentucky 317 



Friersonia iridella (Pilsbry and Frierson). Gravid female from Valles 



River, San Luis Potosi, Mexico 319 



Obovaria retusa (Lamarck). Gravid female from Ohio River, Meigs 



County, Ohio 322 



Nephronaias sapotalensis (Lea). Sterile female from Hueyapam River, 



Vera Cruz, Mexico 327 



Medionidus conradicus (Lea). Gravid female from South Fork of Cum- 

 berland River, Pulaski County, Kentucky 336 



Eurynia (Micromya) iris (Lea). Gravid female from Little Beaver 



Creek, Lawrence County, Pa 341 



Eurynia recta (Lamarck). Gravid female from Lake Erie, Erie County, 



Pa. 



344 



Lampsilis anodontoides (Lea). Gravid female from Rio Grande, Hidalgo 



County, Texas 346 



Lampsilis ovaia (Say). Gravid female from Allegheny River, Armstrong 



County, Pa 350 



Truncilla triquetra Rafinesque. Gravid female from Allegheny River, 



Crawford County, Pa 356 



Truncilla rangiana (Lea). Gravid female from French Creek, 



Armstrong County, Pa 358 



Skull of young specimen of Stenomylus hitchcocki Loomis . . . 369 



