340 KANSAS UNIVERSITY SCIENCE BULLETIN. 



lar in outline, subinflated. Anterior margin straight or 

 slightly incurved dorsally, bluntly rounded below ; ventral 

 margin straight or slightly emarginate ; posterior margin 

 produced below and roundly pointed ; dorsal margin oblique 

 and forming a continuous curve with the posterior margin. 

 Umboidal ratio, nil. Umbones very full and high, and di- 

 rected anteriorly, ornamented with a few coarse ridges. An- 

 terior umboidal slope slightly incurved or straight, very 

 abrupt, lateral margin fully rounded anteriorly and flatly 

 rounded posteriorly, ornamented with a number of coarse, 

 concentric folds, which are variable in their elevation ; pos- 

 terior umboidal slope abrupt, slightly rounded. Epidermis 

 marked with numerous coarse, continuous lines of growth, 

 rusty brown to black in color. Lunule large, ligament thick. 



Interior : Pseudocardinals high, rough, heavy, double in 

 the left and single in the right valve ; the left pseudocardinals 

 sharp, A -shaped ridges, of which the posterior is the longer, 

 meeting at right angles dorsally ; right pseudocardinal a high 

 truncate pyramid arising from a pit. Interdentum broad and 

 short, cut away in the right valve. Laterals heavy, long, ob- 

 lique, slightly curved. Anterior adductor cicatrix rather 

 small, very deep, elongate, semicircular in outline ; posterior 

 muscle scars rather small, deeply impressed, distinct ; dorsal 

 muscle scars extending from the anterior adductor cicatrices 

 to the anterior end of the lateral teeth. Pallial line impressed 

 its entire length. Cavity of the shell not large, of the beaks 

 slight ; branchial impression well marked. Nacre satin-white. 



Length. Height. Breadth. Um. ra. 

 75 53* 47 ' nil. (477.1) 



The range of this species as given by Simpson is the Ohio 

 river, Tennessee, and possibly Claiborne, Ala. This is the 

 first report of its occurrence west of the Mississippi. The 

 one specimen which was found came from a gravel-bed on 

 the Neosho river near the southern state line. 



There is considerable variation in the extent of the folds on 

 the lateral slopes. 



* Taken through region of pseudocardinals. 



