324 KANSAS UNIVERSITY SCIENCE BULLETIN. 



"Animal with the marsupiura occupying the whole outer 

 gills, when filled forming a smooth, very thick, liver-colored 

 pad ; gills free from the abdominal sac from one-half to their 

 entire length ; palpi generally large ; branchial opening pap- 

 illose ; anal opening without papillae, though sometimes 

 very slightly crenulate ; superanal opening generally small, 

 widely separated from the anal." (Simpson.) 



Anodonta imbecillis Say. Plate LXXIV, fig. 1. 



Anodonta imbecillis Say, New Harm. Diss., n, No. 23, 1829, p. 355. 



Anodonta incerta Lea, Trans. Amer. Phil. Soc. v, 1834, p. 46, pi. vi, 

 fig. 16. 



Shell moderate in size, very thin, elliptical, inflated. An- 

 terior margin rounded; ventral margin bowed, sometimes 

 slightly produced posteriorly ; posterior margin roundly 

 pointed, point variable in length and sometimes turned 

 slightly upward ; dorsal margin straight, variable in length, 

 dorsal posterior angle from 145 to 150 degrees. There is a tend- 

 ency to form a dorsal wing. Umboidal ratio, approximately 

 0.30 ; umbones extremely small and flat, marked by several 

 fine broken ridges concentrically arranged. Anterior and 

 lateral slopes rounded ; posterior slope somewhat excavated. 

 Lines of growth continuous, dark in color, infrequent. Epi- 

 dermis smooth and polished, bottle-green to pea-green in 

 color, the umbones a light horn-brown ; postumboidal slope 

 often dark brown, disk often marked with dark green rays. 

 Ligament slight, long. 



Interior : Muscle scars slightly marked, anterior ones the 

 more so ; pallial line sometimes marked. Cavity of shell large 

 of beaks practically none. Nacre silver-white, iridescent over 

 the entire cavity. 



A. imbecillis has a general distribution in all the Mississippi 

 valley, Texas, North and South Carolina. It is found in all 

 the Kansas drainage areas and is plentiful in favored stations 

 in all of them. It is reported by Call as far west as Reno 



