.1913.] NATURAL SCIENCES OF PHILADELPHIA. 259 



PP. — A separating from the hind margin distad to the 

 level of the arculus. 

 R,_Nodus more nearly at one-third of the wing- 

 length, no supplementary sectors between 



Rs and Ms Lithagrion Scudder, 1882 



(Miocene, Colorado). 

 I^I^__Nodus more nearly at one-fourth of the wing- 

 length, at least two supplementary sectors 

 l^etween Rs and Ms. (Supplementary sectors 



from Mia to M4 or Cui) 



Philogenia Selys, 1862, except 

 P. terraha Calv. (Costa Rica to Brazil). 

 <;;GG.— Rs beginning distad to the subnodus, A separating from 

 the hind margin distad to the level of the arculus. 



g_ — Area posterior to Cu2 with usually two or 

 more rows of cells, supplementary sectors 

 from Ml to Cu2 or to hind margin, two 

 cubito-anal cross-veins, the second under the 



quadrilateral 



Paraphlehia hyalina Brauer, 1871 (Mexico). 

 gg^_Area posterior to Cu2 with one row of cells, 

 no supplementary sectors posterior to M4. 

 T — Supplementary sectors from Mia to M4, 

 one cubito-anal cross-vein. 

 Xj._Antenodal cells between M4 and Cui two 

 or three (otherwise as above under RR) 



Philogenia terraha^^ Calvert, 1907 



(Costa Rica). 



UU.— Antenodal cells between M4 and Cui one; 



quadrilateral very long, reaching to the 



level of the nodus 



AUolestes Selys, 1869 (Seychelles). 



TT. — Supplementary sectors from Mia to Ms 



(often none between M2 and Rs), usually 



more than one cubito-anal cross-vein^ 



Dimeragrion new genus (Guiana) .^^ 



'P'P'p^ — Supplementary sectors between M2 and R« 



and (two long ones) between Rs and Ms, 



one cubito-anal cross-vein 



Heteropodagrion Selys, 1885 (Ecuador). 



32 In spite of the fact that Philogenia terraba faUs here, instead of under RR 

 with the rest of the genus Philogenia, the only difference which separates it is the 

 slight one of the more distal position of the separation-point of Rs from Mi +2, 

 and I think this does not entitle terraba to a different generic name. 



9' The genus Ncitragrion Karsch was described from a single female and has 

 been placed under rubric FF above. If additional specimens should prove to 

 have only two antenodals, the genus would fall under TT and would differ from 

 Dimeragrion presumably, at least, in possessing only one cubito-anal cross-vem. 



