238 PROCEEDINGS OF THE ACADEMY OF [May, 



19. Between Cui and Cu2 at the wing-margin are 10-14 rows of cells 



in zoe, seven (front wings) or five (hind wings) rows in ahrogata. 



20. Area posterior to Cu2 le-ss developed and with only two (ahrogata, 



zoe 9 ) or three (zoe cf ) rows of cells. " 



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



the level of the arculus and (b) nearly at the level of the second 

 (distal) cubito-anal cross-vein. 



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



quadrilateral, tivo (one in the front wings of the single female 

 zoe) . 



Comparison of Dimeragrion n. gen. (percubitale n. sp.) with 

 Phenacolestes. 



(D. percubitale 14 6^, 6 9 , British Guiana, Plate XIV, fig. 6.) 



These two genera agree in the characters above numbered 1, 5, 

 7,23 g^ 9^ 12,24 16^^ 16^, 



These two genera differ in characters given below; after each 

 number the difference shown by Dimeragrion is stated. 



2. Twoantenodals.2^ 



3. Postnodals 20-27 (front wing), 16-24 (hind wing), fewer in the 



females than in the males. 



4. Stigma having its proximal edge more oblique. 



6. The veins generally, posterior to Mi, have a slighter caudal 

 curvature, or are almost straight, as they approach the hind 

 margin of the wing. 



10. Between M2 and Rs is but one row of cells which at a distance of 



usually two2^ cells from the '^\-ing-margin increases to two rows. 



11. Rs separates from M1+2 at the first postnodal, or a little proximad 



thereto, or between the first and second postnodals. 



13. Arculus at or very slightlj^ distal to the second antenodal. 



14. M3 separates from M1+2 a little proximad to the subnodus, at 



least at seven-eighths' distance from arculus to subnodus. 2^ 



2- The hind wings of some individuals, c? 9 , of P. duodecima have only one 

 row of cells here. 



-^ Two rows of cells between Mi and Mio for short distances proximad to the 

 level of the stigma have occasionally been noted in Dimeragrion, viz. : for three 

 cells in one front wing each of two males and for two cells in the other front wing 

 of one of these same two males. 



-* Each of the three rows of cells in the terminal part of the area Rs increases 

 to two rows at the wing-margin in one front and one hind wing of the same male. 



-* A third antenodal placed between the usual two and confined to the costal 

 space exists in the right hind wing only of one male. 



-^ This increase to two rows has been noted as beginning at three cells from 

 the margin in 2 front wings and 2 hind wings; at four cells in 3 front wings, 

 1 hind wing; at five cells in 2 front wings, 1 hind wing; at six cells in 2 front 

 wings, 2 hind wings; at seven cells in 1 hind wing. All the individuals, seven 

 in number, showing these variations are males. 



^ In one wing only it separated at the subnodus. 



