302 KANSAS UNIVERSITY SCIENCE BULLETIN. 



Lampsilis gracilis Barnes. Plate LXVII, fig. 4, 



Unio gracilis Barnes, Amer. Jour, of Sci. and Arts, vi, 1823, p. 472. 



Shell large, thin, widely elliptical, not inflated, alate, and 

 sometimes bialate. Anterior margin projecting and rounded ; 

 ventral margin gently and evenly bowed ; posterior margin 

 rounded. Posterior margin winged in young specimens but 

 generally about straight in old ones ; anterior wing small and 

 never present in old specimens. Umboidal ratio variable, 

 0.15 to 0.25. Umbones low and compressed, bearing several 

 coarse, doubly looped ridges, but often worn smooth. Um- 

 boidal slopes flatly rounded, the posterior slightly excavated. 

 Epidermis smooth and shiny or dull and cloth-like ; color 

 dark straw yellow, marked posteriorly with thin bands of 

 dark green ; where cloth-like, dull gray. Lines of growth 

 numerous, continuous, crowded and imbricated posteriorly. 

 Ligament long, fairly stout, dark brown. 



Interior : Pseudocardinals weak, degenerate, thin and plate- 

 like, single in each valve, sometimes mere nodules; laterals 

 weak, short, thin, rather curved. Anterior adductor cicatrix 

 lightly impressed, much longer than wide ; anterior pro- 

 tractor cicatrix very wide and short, lightly impressed. 

 Posterior cicatrices large, very slightly marked, confluent, 

 wider than long. Pallial line slightly impressed anteriorly. 

 Dorsal cicatrices prominent, about seven in number, ar- 

 ranged diagonally across the umbones. Cavity of the beaks 

 slight, of the shell moderate. Nacre rose or salmon-pink 

 umboidally, shading otf into pearl ; iridescent over greater part 

 of the shell : 



L. gracilis has an extended range, being found from eastern 

 Texas to the St. Lawrence, and east in the Hudson river. It 

 is a common species in all river systems of Kansas. Its 

 western range as reported in the Kansas drainage is the 

 Solomon river, and the little Little Arkansas river in the 

 southern drainage. It is often found in the Wakarusa and in 



