66 



Brv'ant Walker 



Marsupial expansion of the female shell of the same texture 



as the rest of the shell 12. 



II. \ Marsupial expansion of the female shell of different texture 

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

 [ tured Tnmcilla. 



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



differentiated with papilke or flaps I3- 



.J 



Inner edge of mantle in front of branchial opening without 



papilla; or fla])s i"- 



Shell smooth M- 



Shell strongly sculptured posteriorly Leiiiio.v. 



Beak sculpture double-looped i5- 



Beak sculpture concentric Carnncnliua. 



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 Lanif^silis. 



Shell inflated, usually higher than long Obuvaria. 



[ Shell subcompressed, longer than high lcti)i:"iaias. 



Genus PTYCHOBRAX'CHUS Simpson, 1900. 



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

 umbonal region rather elevated ; beak sculpture consisting of faint, some- 

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



13- 



14. 



15- 



16. 



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

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

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

 triangular and roughened ; laterals club-shaped, remote. 



