PLATE III 



Fig. 34. Diagram of ventral aspect of head 

 of Hexagenia nymph, portion of 

 left side removed. 



Fig. 35. Diagram of labrum, Ephemerella. 



Fig. 36. Diagram of hypopharynx, Poly- 

 mitarcys. 



Fig. 37. Diagram of hypopharynx, Ecdyu- 



rus. 

 Fig. 38. Diagram of right maxilla, Ecdyu- 



nis. 

 Fig. 39. Diagram of right half of labium, 



Ephemerella. 

 Fig. 40. Diagram of labium, Ecdyurus. 



32 



