CLASSIFICATION 



II 



6. Ephemerida. Metamorphosis direct. Antennae bristle-like. 

 Mouth parts mandibulate, but atrophied in the adult. Prothorax small. 

 Wings membranous, minutely reticulate; hind pair much the smaller, 



A B 



FIG. 18. Pteronarcys regalis. A, nymph (after NEWPORT); B, imago. Slightly reduced. 



B 



FIG. 19. Hexagenia variabilis. A, nymph; B, imago. Natural size. 



