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VOL. 45. 



quite different. Compared with tlie Florissant fossil 0. separata 

 (Scudder), 0. lapidaria is at once separated by the low origin of the 

 branches of the media from the arculus, which is certainly not due to 

 distortion. From the level of the arculus to the lower corner of the 

 triangle there are three full cells, whereas 0. separata and 0. armata 

 show only 2 to 2^. The ends of Mg and M4 and the supplement agree 

 remarkably well with the European fossil 0. metis (Heer), but metis 

 has the branches of the media arising from even a little above the 

 middle of the arculus. The radial sector and its supplement, with 

 the ceUs between, are more like those of 0. metis than those of the 

 living 0. armata. 



Locality. — Miocene shales of Florissant, Colorado, Station 13 B, 

 University of Colorado Expedition; collected by S. A. Rohwer. 



Coty pes. —Cat. No. 59922, U.S.N.M. 



Fig. 1.— OPLONiESCHNA LAPIDAEIA. O, STIGMA; b, TEUNGLE AND ARCULUS; C, ENDS OF VEINS M3 AND M^; 

 d, EADIAL SECTOK AND SUPPLEMENT. 



This specimen puzzled us much, on account of the peculiar origin 

 of the branches of the media from the arculus, a condition not found 

 in the allied species or genera. There are genera, as Planseschna 

 (fig. 2, h, c), in which the origin is below the middle, but these are 

 otherwise quite different; as this character shows no evidence of 

 being abnormal in any way, we can only regard the wing as repre- 

 senting a new species. 



I consulted Mr. E. B. Williamson on some of the characters of tliis 

 species, and he was so kind as to loan me a very fine series of photo- 

 graphs of various Aeshnine genera. Using these with other materials 

 abeady in my possession, I have made a key to the principal 

 genera of Aeshninse, based on the venation. This is given below, 

 and it is hoped that it ^vill be of service in determining fossils, which 

 are usually represented only by the wings. An effort has been made 



