NO. 2000. TWO FOSSIL INSECTS— COCKERELL. 579 



to cite truly generic characters as far as possible, but the specific 

 names are usually given, to show what species were used in the study. 

 In some cases other species were available, but were not included, 

 as they introduced no important additional characters. 



Fig. 2.— a, Oplon^schna separata (ScunrEPO, triangles from two specimens 



COLLECTED AT STATION 14, FLORISSANT; 6, PLAN^SCHNA MULTIPUNCTATA, TRIAN- 

 GLE OF HIND wing; C, PlAN^SCHNA FORCIPATA, TRLVNGLE OF HIND -WXNG. 



It is generally recognized that Oplonaeschna is a relatively primitive 

 member of the Aesbninse; it is therefore interesting to find it in the 

 Tertiary rocks of both America and Europe. Nevertheless true 

 Aeshna, of the modern type, was present in the Miocene of Florissant. 



KEY TO THE PRINCIPAL GENERA OF AESHNINJS, BASED ON THE VENATION. 



(A) Basal space without cross veins. 



(a) Radial sector not branched; branches of media leaving arculus at or near middle 

 [below middle in Oplonaeschna lapidaria]. 



Radial sector separated from supplementary vein below it by one row of cells 1 



Radial sector separated from supplementary vein below it by two tows of cells; triangle 

 of anterior wings much longer and more slender than that of hind (the latter 



only three-ceUed) Allopetalia reticulata [W^illiamson photo.]. 



Radial sector separated from supplementary vein below it by three rows of cells for a 



considerable distance ; triangles of anterior and posterior wings more alike . . 3 



Radial sector separated from supplementary vein below it by four rows of 



cells Oplonaeschna metis (Heer).' 



1. Anal loop of hind wings of three cells; triangle of three cells; [abdomen modi- 



fied] Oligoaeschna [Dolaeschna Needham]. 



Anal loop of hind wings of more than three cells 2 



2. Stigma bounding 1^ cells below; anal loop of 4 cells; triangle of 2 cells. 



Gomphaeschna furcillata . 

 Stigma bounding 2 J cells below; anal loop of 5 cells. (Miocene genus). 



Lithaeschna.'^ 



3. Stigma narrow and elongate, bounding about 4J cells below; triangle of anterior 



wings with three cells Basiaeschna Janata. 



Stigma much shorter and deeper, bounding about 2^ cells below; triangle of anterior 

 wings with six cells Oplonaeschna armata. 



1 This is Aeschna metis Heer, fossil at Radoboj. Handlirsch, following Hagen, refers it to Anax, but 

 Heer's figure shows that this can not be correct. The reference to Oplonaeschna has already been indicated 

 by Needham. I reached the same conclusion before noticing Needham's remarks. 



2 The characters of Idtliaeschna are set forth at length, and contrasted vith those of Gomphaeschna, etc., 

 in Bull. Amer. Mus. Nat. Hist., vol. 23, (1907) pp. 133-136. The triangle of Lithacschna is three-celled by 

 the division of the basal cell, as ia Allopetalia. The genus is perhaps too close to Gomphaeschna. 



