SCAMMON : THE UNIONIDvE OF KANSAS, PART I. 303 



the Kansas river near Lawrence. Its habitat is mud and 

 sand-bars, in deep water with little current. 



The peculiar bialate character of this shell is lost in old speci- 

 mens, but it is very striking in young specimens from favored 

 localities. The most variable character is the degenerate 

 pseudocardiuals, which may be thin, erect, and knife-like, or 

 else absent but for two pearly nodules. The only species with 

 which this one may be confused is L. Istvissima. Ln vissima, 

 however, is much thiner, has a darker nacre and epidermis, 

 and the pseudocardinals are higher and directed obliquely. 



Lampsilis laavissima Lea. Not figured. 



Symphynota Ixvissima Lea, Trans. Amer. Phil. Soc, ill, 1830, p. 444, 

 pi. XIII, fig. 23. 



Shell large, fragile, bialate, rather compressed, broad oval 

 in outline. Anterior margin below the wing strongly curved ; 

 ventral margin strongly bowed ; posterior margin rounded. 

 Posterior wing high, thin, triangular; anterior wing low, 

 triangular. Umboidal ratio, 0.25 to 0.35. Umbones low, 

 pointed, marked with one or two fine concentric ridges, light 

 gray in color. Anterior umboidal slope almost flat ; other 

 slopes quite flatly rounded. Epidermis smooth and shining, 

 varying in color from gray horn to greenish yellow ; young 

 specimens almost covered with fine rays. Lines of growth 

 fine, continuous, imbricated posteriorly, and in old specimens 

 marginally, often indicated only by darker color across the 

 disk. 



Interior: Pseudocardinals thin, plate-like, rather high, 

 triangular in elevation, set obliquely, single in the left and 

 double in the right valve, the dorsal right being very minute. 

 Laterals of moderate length, slightly curved, high, very thin. 

 Anterior adductor cicatrix large, longer than wide, marked. 

 Protractor cicatrix large, faint. Posterior scars large, very 

 faint, confluent. Pallial line faint. Dorsal muscle scars 

 large, faint, ill defined, arranged in a diagonal row across 

 the cavity of the umbone. Lines of growth show plainly 

 as rounded ridges on the inside of the shell. Nacre salmon 

 to purple-pink and very iridescent. 



