PLATE II 



Fig. 

 Fig. 



Fig. 

 Fig. 



Fig. 

 Fig. 



Fig. 



22. Nymph, Epconts humeralis. 



23. Nymph, Hexagenia bilineata, 



24. Nymph, Baetis posticatus. 



25. Diagram of portion of postgena, 

 Hexagenia nymph. 



26. Right mandible, Hexagenia nymph. 



27. Diagram of cross-section of ging- 

 lymous articulation of mandible. 

 Hexagenia nymph. 



28. Diagram of body of right and left 

 mandible of Hexagenia nymph, 

 dorsal aspect. 



Fig. 29. Diagram of right molar surface, 



Ephemerella nymph. 

 Fig. 30. Diagram of left molar surface, 



Ephemerella nymph. 

 Fig. 31. Diagram of left molar surface, 



Ephemera nymph. 

 Fig. 32. Diagram of right molar surface, 



Ephemera nymph. 

 Fig. 33. Diagram of cross-section of righ 



molar surface, Ameletus nymph. 



30 



