LIST OF FIGURES. 



Pages. 

 Snout and lower jaw (mouth open) of Probolodus heterostomus Eigen- 



mann, from above 165 



Ventral fins and protruding spines of Deuterodon acanthogasler Eigen- 



mann 180 



Margarilana margarilifera (Linnaeus). Specimen from the Perl-bach, 



Postfelden, Bavaria 231 



Margaritana monodonta (Say). Specimen from the Cumberland River, 



Kentucky 233 



Left gills of Margaritana monodonta from same locality .... 234 

 Margaritana hembeli (Conrad). Specimen from Hunter's Creek, Cone- 

 cuh County, Alabama 235 



Left gills of another specimen from same locality 236 



Fusconaia rubiginosa (Lea). Male, from South Fork of Tenmile Creek, 



Greene County, Pa 242 



Left gills of Sterile female from same locality 242 



Crenodonta trapezoides (Lea). Male, from Bayou Pierre, De Soto 



Parish, Louisiana 248 



Left gills of Sterile female of Crenodonta trapezoides from Pearl River, 



Hinds County, Mississippi 249 



Quadrula metanevra (Rafinesque). Male from Allegheny River, Arm- 

 strong County, Pa 255 



Left gills of Sterile female of Quadrula metanevra from same locality . 255 

 Rotundaria tuberculata (Rafinesque). Sterile female from Allegheny 



River, Armstrong County, Pa 258 



Plethobasus asopus (Green). Sterile female from Allegheny River, Arm- 

 strong County, Pa 260 



Pleurobema clava (Lamarck). Male from Sandy Creek, Mercer County, 



Pa 265 



Left gills of Pleurobema clava, from Shenango River, Lawrence County, 



Pa 265 



Elliptio crassidens (Lamarck). Male from Allegheny River, Armstrong 



County, Pa 267 



Left gills of sterile female from same locality 267 



Unio piclorum (Linnaeus). Male from Saale River, Rudolstadt, Germany 274 

 Left gills of sterile female of Unio piclorum, same locality . . 274 



vii 



