70 T. D. A. Cockerell — Descriptions of Tertiary Insects. 



agrion. Characteristic of both is the position of vein M s , 

 originating a long way before the level of the nodus, though 

 not half-way to the arculus ; — a condition found to-day in 

 Megaloprepus, one of the Anormostigmatini. The question 

 was raised, whether Lithagrion and Melanagrion could rep- 

 resent the stem which gave rise to the Anormostigmatini ; but 

 altogether against this is the position of the long sector between 

 veins M 1 and M 2 . Mr. E. B.Williamson writes that he regards 

 the latter character as of considerable significance, and for this 

 and other reasons would support Scudder's reference of the 

 insects to the Podagrion series. He adds, with reference to 



Fig. 1. Lithagrion hyalinum. 



M. umbratum : " it is not specialized by reduction, and the 

 nodus is retracted as in Paraphlebia (but not so much as in 

 Anormostigmatini), with which compare the more specialized 

 Argiolestes and iVcsolestes, for example." 



The following table separates the three Florissant species : 



Wings hyaline ; stigma bounding 3-J-3f cells below. 



Lithagrion hyalinum Scudd. 

 Wings strongly infuscated ; stigma bounding 5 cells 

 below. ... 1. 

 1. Apex of wings hyaline ; costal cells narrow. 



Melanagrion umbratum (Scudd.). 

 Apex of wings dark ; costal cells broad. 



Melanagrion nigerrim,um Ckll. 



Enallagma florissantella sp. nov. Figure 2. 



Wing hyaline, about 23 mra long (base gone) ; nodus to stigma 

 12-J mm ; nervures and stigma dark sepia 



brown ; subnodus 



oblique; subquadrangle not crossed ; 14 costal sectors between 

 nodus and stigma ; stigma bounding one cell below ; costal 

 cells beyond stigma large ; only one double cell in the series 

 between M 1 and the sector M ia , this immediately below stigma, 

 separated therefrom by a single cell ; three cells between 

 quadrangle and level of nodus, the third very long, and 

 represented by two cells in the series immediately below ; 



