67 



e. Lateral spines of 9 about twice as long as those of 8 ; 

 length of ventral surface of 9 at middle about one 

 half its basal width ; abdomen more than thrice as 

 long as broad. 6. vastus, 



d. Lateral spines of 9 slender, elongate-acuminate, incurved 

 apically, nearly or quite as long as the distance to the 

 median tooth of the segment ; labial apical hook not 

 projecting beyond the teeth. 9. extermis. 



AA. Three pairs of lateral spines, the first pair very small; 

 teeth of lateral labial lobes mostly distinctly separated 

 by rather deep incisions, and obliquely truncate; medi- 

 an lobe rather prominent, a small projecting tooth at 

 middle ; side margins of 9 entire, more or less fringed 

 with soft hairs, 10 (except in spieatiis) as long as, or 

 longer than, wide ; only a trace of a median posterior 

 tooth on 9. {Arigomphus Needh.) 

 ff. Last three segments evenly tapering, length of ventral 

 surface of 9 at middle about three fourths of its basal 

 width, 10 wider than long ; traces of dorsal hooks ; 

 labial apical hook prominent, toothed on its inner 

 side but not appearing bifid. 10. spicafus. 



f. Last three segments concavely tapering, length of ventral 

 surface of 9 at middle about equaling its basal width, 

 10 longer than wide ; a low scurfy median abdominal 

 ridge. 

 (j(j. Labial apical hook as in spicatus', lateral spines of 9 

 not over one fifth as long as the inferior append- 

 ages. 11. austral is. 

 g. Labial apical hook and outermost tooth united to form 

 a prominent bifid apical tooth. 

 Jtli. Lateral spines of 9 not over one fourth as long 

 as posterior appendages, 12. vUlosipes. 

 h. Lateral spines of 9 about as long as inferior append- 

 ages. 13. pallid us. 

 A. Four pairs of lateral spines (minute in spiniceps); labial api- 

 cal hook large and strongly incurved ; teeth few, 0-5, 



