138 TERTIARY INSECTS OF NORTH AMERICA. 



The American fossil species of Agrion which are represented by their 

 wings may be separated as follows : 



Table of the species of Agrion. 



Four anteuodal cellules below the short sector; auteuodal portion of the costa scarcely arched. 



1. A. mascescens. 

 Three antenodal cellules below the short sector ; anteuodal portiou of the costa noticeably arched. 



'i. A. exsitlaris. 



1. Agrion mascescens. 



PI. 13, Figs. 8, 9. 



This species is represented by a pretty well preserved specimen and 

 its reverse showing most of the body, a part of the legs and the wings, but 

 the latter confused by the overlying of those of one side upon those of the 

 other. Tlie head is preserved only enough to show its form, which has 

 nothing peculiar, and the same may be said of the thorax. Seven joints of 

 the slender abdomen are pi-eserved, the second of which indicates that the 

 specimen is a male. The head and thorax with the legs are black, but the 

 abdomen is colorless; the legs are doubled up, the femora about as long as 

 the breadth of the head, and the tibial spines, of which there are seven or 

 eight in a row, are a little shorter than the interspaces between adjacent 

 ones The wings are scarcely depressed at the nodus, the antenodal por- 

 tion of the costal margin almost straight, hyaline with black veins, the 

 pterostigma normal, rhomboidal, slightly longer than broad, alike on both 

 wings, the only difference being in a slightly greater obliquity of the outer 

 and inner margins (and especially of the outer) and the slightly shorter 

 lower margin in the front wing ; very pale fuliginous, fading out towards 

 the margins, margined with heavy blackish veins, surmounting a single 

 cellule. The inferior sector of the triangle originates far before the basal 

 postcostal nervule, which is situated slightly nearer the second than the first 

 antecubital nervule. The arculus is directly beneath the second antecubital 

 nervule. There are apparently eleven postcubitals on the fore wing and 

 there are ten on the hind wing. Quadrilateral of the fore wings with the 

 inner and upper side of similar length and half as long as the lower side ; 

 on the hind wings the inner side is considerably shorter than the upper, and 

 the latter nearly three-fifths the length of the lower ; four antenodal cellules 

 below the short sector ; the petiolation begins unusually near the base of the 

 wing or considerably before the first antecubital nervure. The nodal orig- 



