300 KANSAS UNIVERSITY SCIENCE BULLETIN. 



which it is most common, the shell has been reported as far 

 west as the Solomon river. It is sometimes found in the 

 Marais des Cygnes, at Melvern, and from there east. It is 

 reported only from the Neosho river and its tributary. Fall 

 river (Popenoe), in the southern drainage. Here it is re- 

 placed in the main by L. purpwrata, which is better fitted to 

 survive the conditions present there. Its habitat is muddy 

 river-beds, in deep water — generally confined to the larger 

 streams. 



When in good condition this is one of our most beautiful 

 luios. The variation is confined principally to the color of 

 the epidermis and the nacre. This has been covered in the 

 description above. Alata may be confused with two other 

 forms — /-. purpurata and hrvisxi ma. From jiurpiirata it ma.y 

 be separated in well-preserved specimens by its high wing, 

 but in old specimens this is often almost gone. It is, how- 

 ever, a lighter shell, less swollen, and almost square behind, 

 while purpurata is rounded. The pseudocardinals are lighter 

 in alata. La vissima is much thinner and more rounded than 

 alata, and the pseudocardinals in the former are reduced to 

 a thin erect plate in each valve. 



Lampsilis purpurata Lamarck. Not figured. 



Unio purpurata Lamarck, An. sans Vert., vi, 1819, p. 71. 



Unio ater Lea, Trans. Amer. Phil. Soc, in, 1830, p. 42G, pi. vn, fig. 9. 



Shell large, fairly thick, particularly anteriorly and outside 

 of the pallia! line, elliptical slightly alate ; females inflated, 

 males less so. Anterior margin projecting and decidedly 

 rounded; ventral margin straight, showing a very slight 

 tendency to become emarginate centrally ; posterior margin 

 rounded, but tending to become biangulate dorsally ; dorsal 

 margin a low, thick wing. Umboidal ratio, 0.15 to 0.30. Fm- 

 bones large, swollen, rounded, marked in young specimens 

 with a series of five or six v -shaped ridges. Umboidal slopes 

 all fully curved, lateral showing a very faint furrow veu- 

 trally ; on the posterior slope are two more or less distinct 

 raised lines running from umbone to posterior margin. Epi- 

 dermis smooth and shiny over and below the umbones, but 

 roughened by the imbrications of the lines of growth margin- 



