1913.] NATURAL SCIENCES OF PHILADELPHIA. 239 



15. Between ]Mi-3 and M4 are (a) no cross-veins proximal to the 



level of the subnodus, and (b) between Ms and jM4 is only one 

 row of cells to the wing-margin. 



17. Between M4 and Cui are (a) two to three antenodal cells {sensu 



Sehjsii) and (6) only one-^ row of cells to the wing-margin. 



18. Cubito-anal cross-veins between the levels of the two antenodals 



varying from . one to four, most frequently two ; often an 

 additional cross-vein proximal to the level of the first antenodal.-'* 



19. Between Cui and Cu2 is only one row of cells to the wing-margin. 



20. Area posterior to Cu2 with only one row of cells. 



21. Anal vein separating from the hind wing-margin (a) distad to the 



level of the arculus and (6) distad to the level of the cubito-anal 

 cross-vein or veins. 



22. Anal cross-veins, proximal to the level of the distal end of the 



quadrilateral, one, situated a little proximad to the oblique 

 vein which continues the distal side of the quadrilateral caudad, 

 or at that oblique vein. 



Comparison of Heteragrion (tricellulare) with 

 Phenacolestes. 



(H. triceUulare cf , Guatemala.)'"' 



These two forms agree in the characters above numbered 0, 7, 8, 



16, 18, 21a. 



These two forms differ in characters given below ; after each number 

 the difference shown by the Heteragrion is stated. 



1. Nodus at one-fourth. of the wing-length. 



2. Only two antenodals. 



3. Postnodals 21-25. 



4. Proximal edge of pterostigma more oblique, but the difference is 



less marked than in Thaumatoneura. 

 6. Longitudinal veins hardly curved at all caudad on approaching 



the wing-margin. 

 9. M2 separates from Mi at three-sevenths ( = .43) of the distance 



from nodus to stigma. 



10. Between M2 and Rs at the wing-margin is but one row of cells. 



11. Rs separates from M1+2 far distad {e.g., five to six cells) to the 



subnodus. 



12. Between Rs and M3 at the wing-margin is but one row of cells. 



13. Arculus at the second antenodal. 



14. Ms separating from M1+2 at or barely proximad to the subnodus. 



15. Between Ms and M4 are (a) no cross-veins proximal to the level 



of the subnodus, as results from No. 14, and (6) at the wing- 

 margin only one row of cells. 



28 Two rows exist in both hind wings of each of two females and in one hind 

 wing of one male. 



2^ For details see the specific description of Dimeragrion percubitale, postca, p. 269. 



30 The wing of Heteragrion flavovittatum has been figured by Xeedham {Geneal. 

 Study, pi. 53, fig. 6). 



