144 Trans. Acad. Sci. of St. Louis. 



Lampsilis alata Say. 



PI. XI. f. 1,1a. 



Figure 1 illustrates the interior of the right valve of the 

 specimen. A fold starts 15 mill, from the umbo and extends 

 to the lower margin of the shell where it ends in a bell-shaped 

 expansion; the fold is 45 mill, long and the greatest diameter 

 is 22 mill. Near the starting-point there is a projection 

 which forms a large bunch extending into the cavity of the 

 shell. The left valve (fig. la) is normal, except for a 

 slight constriction which extends across the shell in a direc- 

 tion parallel with the fold in the right valve. 



The writer is quite unable to explain the cause of this mal- 

 formation. Some peculiar accident must have occurred to the 

 shell to have caused such a peculiar mode of growth. With- 

 in the bell-shaped fold the epidermis is formed, but it is 

 rougher than that of the rest of the shell. The breadth of 

 the shell is greater than in a normal specimen of this species 

 and the posterior margin is more rounded. The posterior 

 basal portion of the shell projects far below the normal ventral 

 margin of the shell, as in female specimens of Lampsilis 

 luteola. 



Length 87.00; Height 65.00 ; breadth 34.00 mill. 



Lampsilis ligamentina Lamarck. 



PL XI. /. 3, 5. 



A single specimen of this species seems to have been crushed 

 in on the posterior end of both valves, probably by the feet of 

 horses or cattle. This injury caused a hole on each side of 

 the shell, 40 mill, behind the umbones, which the animal 

 neatly repaired by the addition of new shelly matter. The 

 injury to the left valve was greater than to the right, the shell 

 being pushed in to such an extent as to make an oblong hole 

 at the anterior edge of the posterior adductor muscle scar. 

 It is notable that the epidermis formed about the injured 

 region is much coarser than that on the normal part of the 

 shell and is raised in fine ridges. This seems to be a general 

 rule in such cases. 



Length 85.50; height 56.00; breadth 43.50 mill. 



Another specimen of this species (a right valve, fig. 3) is 

 abnormally thickened and ridged internally by the addition of 



