Shell more coarsely marked, not regularly rhombic ovate. 

 Transversely elongated. 



Umbones quite full. About 15 to 20 x 10.75 x 7.75 mm. 



S. sulcatum (Lam.) Pr. 

 Shell inflated, about 17 x 12 x 9 mm.; polished. 



*S'. simile Say. 



Shell duller, less inflated, about 15 to 20 x 10.75 x 7.75 

 mm, S. s^dcatum (Lam.) Pr. 



Umbones but slightly inflated; about 14 x 10.75 x 7.75 mm. 



S. solidulum Pr. 



Shorter, nearly equilateral; umbones full; dimensions about 

 10.75 X 7.75 X 6.25 mm. S. striatinum (Lam.) Pr. 



45. — Lampsilis (In this and the following genera only the species found 

 in the region under discussion are included.) 



Shell distinctly winged above hinge; flattened, rather heavy, large; 



nacre purple. L. alatus (Say) Bak. 



Shell not winged, more or less inflated. 



Very ventricose, rather thin ; umbones prominent, but angular 

 or ridged. L. ventricosus (Barnes) Bak. 



More elongated, less inflated in umbonal region, sometimes near- 

 ly cylindrical. 



Less than 4 cm. long, dark. L. parvus (Barnes) Bak. 



More than 5 cm. long. 



Length more than twice the height. 

 Epidermis almost or quite black. 



Length 8-10 cm.; shell rather thin; nacre white or 

 bluish. L. suhrostratus (Say) Simp. 



Larger; shell heavy; nacre purple or nearly white. 



L. rectus (Lam.) Sm. 

 Epidermis yellow. L. anodontoides (Lea) Bak. 



Length less than twice the height. 

 Umbones quite prominent. 



Epidermis yellow, shiny, usually rayed; fe- 

 male shell expanded posteriorly. 



L. hiteolus (Lam.) Bak. 

 Epidermis darker, not as highly polished, 

 with or without rays; umbones less prom- 

 inent. L. Ugamentinus (Lam.) Smith 

 Umbones depressed, shell compressed and tap- 

 ering posteriorly. L. ellipsiformis (Con.) Simp. 



4:6.—Unio gihhosus Barnes. 

 47. — Quadrula 



Shell tubercled or plicate. 

 Plicate, without tubercles. 



Umbones prominent; shell about 10.9 x 8.1 x 5.9 cm. 



Q. plicata (Say) Bak. 



87 



