412 Annals Entomological Society of America [Vol. VI ^. 



EXPLANATION OF PLATES. 

 Plate LXIL 

 Fig. L Mature nymph of Blasturus cupidus. 

 Fig. 2. Male imago of Blasturus cupidus just after transforming. The cast 



sub-imago skin shows the dark wing-pads. 

 Fig. 3. Ameletus ludens. 



Fig. 4. Nymph of Epeorus humeralis. The hind wing-pads may be seen through 

 the transparent front ones. 



Plate XLIIL 

 Fig. 5. Nymphs of Callibaetis fluctuans, climbing about in their natural habitat. 

 Fig. 6. Male sub-imago of Callibaetis fluctuans just emerged. 



Plate XLIV. 

 Fig. 7. Half grown nymph of Potamanthus bettini. 

 Fig. 8. Mature nymph of Ephemera. 



Fig. 9. Male imago of Hexagenia bilineata showing a posture of the fore legs 

 characteristic of the males of many May-flies. 



Plate XLV. 

 Fig. 10. Right gills of Lleptagenia interpunctata. The first gill is turned with 



the lower side up and the fimbriate division is fully exposed; in the 



others it is indicated through the transparent lamella. 

 Fig. 11. Right gills of Epeorus humeralis, upper surfaces. When in the natural 



position the spinose border is in contact with the surface upon which 



the nymph rests. 



Pl.\te XLVL 

 Fig. 12. Right gills of Iron'fragilis, upper surface, gills turned backward in natural 



position. 

 Fig. 13. Right gills of Chirotonetes albomanicatus, under surface, gills turned 



forward. 



Plate XLVIL 

 Fig. 14. Mouth-parts of Callibaetis fluctuans. a, right, and d, left mandible; 



b, labrum; c, hypopharynx; e, right maxilla; f, labium. 

 Fig. 15. Maxilla of Tricorythus allectus. 



Figs. 16 and 19. Right and left mandibles of Ephemerella lata. 

 Fig. 17. Left maxilla of Ephemerella serrata. ' 

 Fig. 18. Left maxilla of Ephemerella deficiens. 



Plate XLVIIL 

 Figs. 20 and 21. Right and left mandibles of Tricorythus allectus. 

 Fig. 22. Labium. 

 Figs. 23 and 24. Right and left mandibles of Potamanthus bettini. 



Plate XLIX. 

 (Structures of nymph of Hexagenia). 

 Fig. 25. Maxilla. 

 Fig. 26. Second right gill. 

 Fig. 27. First right gill. 



Fig. 28. Labrum (La) and Clypeus (CI), outer aspect. 

 Fig. 29. Labrum (La) and Clypeus (CI), inner aspect, showing the epipharyn.x. 



lying partly upon the clypeus and partly upon the labrum. 

 Fig. 30. Antenna. 



Fig. 31. Right mandible, outer aspect. 

 Fig. 32. Right mandible, inner aspect. 



Fig. 33. Hypopharynx, under side, showing lingua and superlinguae. 

 Fig. 34. Grinding surface of left molar. 

 Fig. 35. Grinding surface of right molar. 

 Fig. 36. Left mandible, inner aspect. 

 Fig. 37. Left mandible, outer aspect. 

 Fig. 38. Labium outer aspect. 



