60. Length of shell more than two times the height 61. 



Length less than two times the height 70. 



6L Shell usually with small transverse ridges on the posterior slope; epider' 

 mis with broken rays (color markings) ; nacre bluish to salmon tinted; 

 less than three inches; Tennessee and Alabama River drainage 

 Medionidus conradicus (Lea) 

 No transverse ridges on the posterior slope; becoming larger 62. 



62. Laterals much removed from the cardinals, with no connecting plate; 



posterior ridge ending below the mid line, with two radiating furrows 

 on the flattened posterior slope; umbonal markings six to ten concentric 

 ridges curved up and drawn together behind; central states 

 Elliptio tetralasmus (Say) 

 Uniomerus tetralasmus (Say) 

 Either with the laterals connected with the cardinals by an interdentum 

 or with the posterior ridge ending at the mid line or above; umbonal 

 markings not as above 63. 



63. Posterior ridge ending at a point midway or more up from the base; 



beak cavity shallow but impressed; umbonal markings double-looped 



and open behind 64. 



Posterior ridge ending at the posterior basal angle; little, if any, beak 



cavity; umbonal markings irregular bars 67. 



64. Shell with a curved posterior ridge ending in a slightly narrowed area; 



epidermis dull; Atlantic drainage 



Lampsihs nasuta (Say) Beaked Shell 

 Ligumia nasuta (Say) 

 Posterior ridge straight; posterior end evenly rounded or pointed 65. 



65. Epidermis olive, brown or black, rayed only in young; shell heavy; with 



three to five double loops on the umbones; nacre purplish to salmon; 

 central and eastern states 



Lampsihs recta (Lamarck) Black Sand Shell 



Ligumia recta (Lamarck) 

 Epidermis clear yellowish or darker and with rays; shell thinner; um' 

 bones with eight to ten fine double loops; nacre white to salmon tint' 

 ed; Mississippi drainage and Gulf states 66. 



66. Epidermis clear yellowish 



Lampsilis teres (Raf.) Yellow Sand Shell 

 Lampsilis anodontoides (Lea) 

 Epidermis greenish, rayed 



Lampsilis teres^fallaciosa Simpson Slough Sand Shell 

 Lampsihs falhciosa Simpson 



67. Epidermis tawny; rays, if present, broken; nacre white, with oblique 



folds; east-central states 



Ptychohranchus fasciolare (Raf.) Kidney Shell 

 Epidermis dull to dark; rays, if present, complete; nacre usually purphsh 



68. 



68. Hinge plate thin; shell usually very long and narrow, often as much as 



three times as long as high; east-central states 

 Elliptio productus (Conrad) 



156 



