NEDROPTERA— ODOXATA— AGRIONINA. 135 



oblique in tlie same sense. Reticulation dense, mostly tetragonal except- 

 ing in the region of the supplementary sectors of which there are two be- 

 tween each pair of sectors from the ultranodal to the short sector, excepting 

 in the interspace between the subnodal and the median ; none excepting 

 the upper ones are curved, and there is also a single very brief one between 

 the short sector and the superior sector of the triangle Postcostal space 

 simple or nearly so, the inferior sector forming it extending beyond the mid- 

 dle of the wing but not reaching the border. Wings enlarging considerably 

 towards the middle, strongly petiolate nearly to the base of the quadrilateral; 

 this is several times longer than broad, enlarging slightly away from the 

 base, the lower side from a fourth to a third longer than the upper. Nodus 

 situated about one-third the distance from the base to the pterostigma. 



This genus is closely allied to Philogenia and Podagrion, the subnodal 

 and median sectors having a similar origin, but it is clearly distinct from 

 either; it differs from the former in the structure of the pterostigma, which 

 nowhere departs from the costal margin, in the straightness of the supple- 

 mentary sectors, the obliquity of the apex of the quadrilateral, the greater 

 distance of the nodus from the base of the wing and the less petiolated and 

 more bi'oadly expanded form of the wing. In the number and position of 

 the supplementary sectors, however, it closely resembles it. From Pod- 

 agrion it differs in the earlier departure of the nodal from the principal 

 vein, the larger number of cellules below the pterostigma, the much greater 

 nuniber of supplementary sectors, and the more broadly expanded wing ; it 

 resembles it rather than Philogenia in the structure of the pterostigma, the 

 petiolation of the wing, and the position of the nodus. It differs even more 

 from Dysagrion, which I have placed in the same groixp, than from either 

 of these two recent genera. Two species have been discovered, both from 

 Florissant. 



Table of the species of Litliagrioii. 



Wings clear; postcubitals few 1 L. hiialinum. 



Wings clouded except at base and apex; postcubitals numerous 2. L. iimhraliim 



1. LiTHAGRION HYALINUM. 



PI. 13, Fig. 4. 



A pair of wings, barely overlapping at the postcostal margin and with 

 the tips broken beyond the middle of the pterostigma, but otherwise in 

 admirable preservation, represent this species; they appear to be upper wings. 



