EXPLANATION OF PLATE VIL 



Fig. 15. — Anodonta grandis Say 9 — Actual longi-section of the vis- 

 ceral mass showing entire alimentary tract, protractor muscle and other 

 animal structures in left valve. (^ Nat. size). 



Fig. 16. — Megalonaias heros (Say) 9 Photograph of gravid specimen 

 showing animal structure in left valve. (^4 Nat. size). 



