290 KANSAS UNIVERSITY SCIENCE BULLETIN. 



with numerous continuous coarse lines of growth which soon 

 lose the triangulate character of the posterior margin as they 

 approach the umbones, and so form one rounded curve pos- 

 teriorly. Epidermis dark straw color in the young speci- 

 mens and deep brown in the old ; dark green rays of variable 

 width run from the beaks to the ventral margin in young 

 specimens and sometimes occur obscurely in old ones. Liga- 

 ment very large, robust, dark brown. 



Interior : Pseudocardinals massive, rather low, rounded 

 serrate, double in the left and right, the right anterior being 

 rudimentary. Laterals of variable length, curved, coarse, ser- 

 rate. Interdentum of very variable length and width. An- 

 terior adductor cicatrix deep, longer than wide, rough, set 

 under the anterior pseudocardinal in the left valve ; pro- 

 tractor cicatrix longer than wide, quite deep. Posterior scars 

 large, impressed, confluent. Pallial line impressed anteriorly. 

 Dorsal muscle scars large and deep, in the cavity of the beaks 

 or on the lower surface of the interdentum, sometimes on the 

 base of the anterior pseudocardinals. Cavity of the beaks 

 moderate, of the shell rather large. Nacre, satin-white to 

 salmon-pink, the last less common, somewhat iridescent pos- 

 teriorly. 



Lampsilis ligamentina var. gibba Simpson. Not figured. 



Unio crassus Sowerby, Conch. Icon, xvi, 1868, pi. xcv, fig. 520. 



Lampsilis ligamentinus, var. gibbus Simpson, Proc. U. S. Museum, 

 1900, vol. xxn, p. 540. 



To be distinguished from the true species by the greater 

 prominence of the umboidal ridge and the fusing into one 

 curve of the posterior and dorsal margins. This gives the 

 specimens a peculiar humped appearance. The variety is 

 generally smaller and darker colored, and the nacre is more 

 frequently tinted with salmon. 



Ligamentina is found in the entire Mississippi drainage, 

 southern Michigan, western New York, and Ontario. The 

 variety gihba occurs south from the Ohio river. The species 

 proper occurs in all the Kansas drainage systems, but in the 



