Vol. XXVli] ENTOMOLOGICAL NEWS. 329 



Acanthagrion aduslum Williamson, figs. 20-21. A thin septum-like, 

 median, internal hook pointing distad on segment 3. 



Acanthagrion apicale Selys., figs. 3-4. Segment 3 with a pair of 

 heavy, chitinized, terminal hooks between which is a median globular 

 swelling. 



Acanthagrion ascendens Calvert, figs. 12-13. A median internal api- 

 cal hook on segment 3. 



Acanthagrion chclifcrum Selys., figs. 26-27. An internal median 

 swelling on segment 3. A thin, chitinized median hook on segment 

 2. Terminal fold well developed. The ridges in fig. 27 may have been 

 due to the drying of the preparation. 



Acanthagrion cuyabae Calvert, figs. 16-17. A median internal enlarge- 

 ment between the two lateral lobes of segment 3. 



Acanthagrion "gracilc" Rambur, figs. 8-9. Peculiar in that the tip of 

 segment 3 is divided horizontally into three septa. 



Acanthagrion indcfensum Williamson, figs. 22-23. A delicate me- 

 dian, internal, barbed hook on segment 3. 



Acanthagrion interruption Selys., figs. 5-7. A median internal hook 

 on segment 3. See fig. 7. 



Acanthagrion kennedii Williamson, figs. 14-15. A thin septum along 

 the median, internal line of segment 3. 



Acanthagrion latcrale Selys., figs. 18-19. The most simple of the 

 series having merely an internal, median swelling to indicate its re- 

 lationships. 



Acanthagrion temporale Selys., figs. 1-2. A thin septum as in ken- 

 nedii. 



Acanthagrion truncatum Selys., figs. 24-25. A median internal hook 

 formed by the turning in of the edges of segment 3. 



In conclusion, certain venational characters divide this 

 genus, as it has been understood in the past, but the penis, be- 

 cause of its evident great variety of forms, is of little assist- 

 ance in defining groups among this series of species. How- 

 ever the study of the penis has shown very definitely that we 

 are dealing with structurally, well defined species rather than 

 with subspecies and varieties based, as hitherto, largely on 

 color. 



In addition I might say that I shall treat in another paper 

 of a series of species in which a condition exists just opposite 

 to this which occurs in Acanthagrion. In this other series 

 what are apparently generically distinct species have almost 

 identical penes. 



