32. Epidermis shining, with narrow and wide rays, except in old shells; teeth 



heavy; Atlantic drainage 



Alasmidonta undulata (Say) 

 Epidermis dull, with obscure rays; teeth small 33. 



33. With one to three blurred laterals in each valve; shell pointed behind; 



eastern states 



Alasmidonta heterodon (Lea) 

 Laterals almost completely absent; shell blunt behind; Tennessee River 

 drainage 



Alasmidonta hadia (Raf.) 



Alasmidonta holstonia (Lea) 



34. Shells with ribs, pustules, knobs or spines 35. 

 Shell relatively smooth, except for the posterior ridge 55. 



35. Shell ridged (ridges not crowned by rows of knobs or pustules) 36. 

 Shell with pustules, knobs or spines 40, 



36. Shell with but two ridges, one median and one posterior, with a much 



depressed area between; Ohio River drainage 

 Dysnomia fiexuosa (Raf.) Folded Shell 

 Dysnomia foliata (Hild.) 

 Shell with three or more ridges on each valve 37. 



37. With a sharp posterior ridge; nacre purple, red or coppery; south-central 



states 



Amhlema domheyana (Val.) Bank Climber 



Plectomerus domheyana (Val.) 

 Little or no posterior ridge; nacre usually white, tinted towards the 

 post-basal angle 38. 



38. Lower umbonal region with small zigzag ridges or indications of pustules; 



shell getting to be large and heavy; Mississippi drainage 



Amhlema gigantea (Barnes) Giant Washboard, Sugar Shell 

 Is/Legalonaias gigantea (Barnes) 

 Lower umbonal region relatively smooth except for the beginnings of 



the large oblique folds; shell smaller; Mississippi drainage 39. 



39. Umbones reaching well above the hinge line; larger rivers of the Missis- 



sippi drainage 



Amhlema plicata (Say) Blue Point 

 (Amhlema peruviana (Lamarck) ) 

 (Amhlema rariphcata (Lamarck) ) 

 Umbones reaching scarcely above the hinge line; smaller streams of the 

 Mississippi drainage 



Amhlema plicata-costata Raf. Washboard, Three Ridge 

 Amhlema costata Raf. 



40. With long upright spines; Georgia 



Canthyria spinosa (Lea) Spiny Shell 

 Elliptio spinosus (Lea) 

 With knobs or tubercles 4L 



4L Length over one and one-half times height; anterior part with or with- 

 out pustules 42. 

 Length usually less; no pustules anteriorly 43, 



152 



