56 Bryant Wai,ke;r 



Marsupial expansion of the female shell of the same texture 



as the rest of the shell ■ i^. 



II. -j Marsupial expansion of the female shell of different texture 

 * I from the rest of the shell and usually radiately sculp- 

 [ tured Trnncilla. 



' Inner edge of the mantle in front of the branchial opening 



differentiated with papillfe or flaps I3- 



12.^ ... 



Inner edge of mantle in front of branchial openmg without 



papillae or flaps ^^^ 



\ Shell smooth I4- 



13- i 



I Shell strongly sculptured posteriorly Lennox. 



14. 



15- 



Beak sculpture double-looped i5- 



Beak sculpture concentric Carnnculina. 



Inner edge of mantle in front of branchial opening in female 



distinctly papillate Bnrynia. 



Inner edge of mantle in front of branchial opening in female 



with a ribbon-like flap Lampsilis. 



r Shell inflated, usually higher than long Ohovaria. 



16. <^ ' ... 



[ Shell subcompressed, longer than high Actinonaias. 



Genus PTYCHOBRANCHUS Simpson, 1900. 



Shell triangular, solid, sometimes becoming arcuate in old specimens; 

 umbonal region rather elevated; beak sculpture consisting of faint, som.e- 

 what broken ridges, which have a tendency to be doubly looped ; posterior 



Fig. 187 



ridge rounded, but well developed; epidermis usually painted with wavy 

 hair-like ra,ys or broken, radiating bars, which show a tendency to form 

 square spots; hinge-plate rather wide and flat; pseudocardinals small, low, 

 triangular and roughened; laterals club-shaped, remote. 



