MOUTH PARTS OF THE NYMPH. 



definite as are furnished by other organs, 

 key: 



These are summarized in the following 



I. Mandible With Tusk. 



A. Tusk shorter than mandible proper, tf.* 23. 

 AA. Tusk longer than mandible proper. 



(a) Tusk with spines, and out curved 

 (b) Outer edge serrated, tf. 12. 

 (bb) Outer edge not serrated, tf. 17. 

 (aa) Tusk without spines 

 (b) Tusk incurved 



(c) Outer edge serrated, tf. 24. 

 (cc) Outer edge not serrated; hairs long 

 and abundant, tf. 21. 

 (bb) Tusk nearly straight, very slightly out 

 curved at tip, tf. 14. 



II. Mandible Without Tusk. 



A. Outer canine with large teeth. 



(a) Outer canine with 5 teeth, tf. I 1 '; inner canine 

 with 4 teeth, 

 (aa) Outer canine with 4 large teeth. 



(b) Inner canine with 5 teeth, tf. 18. 

 (bb) Inner canine with 4 teeth, tf. 22. 

 (bbb) Inner canine with 3 teeth. 



(c) Outer edge of mandible straight, or 

 nearly so, tf. 3. 

 ( cc ) (inter edge of mandible distinctly 

 curved. 

 id) Outer edge of mandible with 

 a distinct curve from base 

 to apex, tf. 8; lacinia 

 bluntly cone-shaped, with 

 short hairs at tip. 

 (dd) Outer edge of mandible with 

 a distinct curve at the 

 apex ; lacinia with long 

 hairs at the tip, tf. 10, 25. 

 (bbbb) Inner canine with 2 teeth. 



(c) Outer edge of mandible with a dis- 

 tinct curve near the base, and with 

 long spines, tf. 13. 



EPHEMERINA1-. 

 Potamanthus. 



Pentagcn'm. 

 Ephemera. 



Polymitarcys. 



Euthyplocia. 

 Hexagenia. 



BAETINAE. 



. imeletus. 



Callibactis. 

 Baetis. 



Siphlurus. 



Cacnis. 



Blasturus. 



Tricorythus. 



Hi., text figure. 



14 



