XVI] THE GEOLOGICAL RECORD 315 



Many beetles and flies occur; also the larvae of Plectoptera, 

 Chironomus and other aquatic insects. Dragonflies are not 

 common, and not all of them well-preserved. 



The question of altitude is a very interesting one. At the 

 present day, no Libellulinae, Gomphinae or Calopterygidae reach 

 a high elevation in a climate like that which Florissant possessed. 

 A typical high-altitude Odonate fauna would consist of Corduliinae, 

 Aeschninae and Agrionidae. The two latter groups only have so 

 far been found at Florissant. We may therefore conclude that 

 the lake lay at a considerable altitude in Miocene times, even as 

 its remains do to-day. 



The Odonata of Florissant have been chiefly collected and 

 described by Scudder [148, 149] and Cocker ell [43-47]. The Aeschninae 

 all appear to belong to the older genera of the tribe Aeschnini, such 

 as Oplonaeschna, having an unbranched Rs and a long pterostigma. 



Fig. 164. Fore-wing of Phenacolestes mirandus Scudder ( x 1), Miocene, Florissant. 

 Original restoration from nearly complete 'wings figured by Calvert. 



The Agrionidae are of greater interest, since it is here that we 

 find positive evidence of the former existence of a stage in the 

 evolution of that family, in which the reduction of the prenodal 

 area was still incomplete, and the number of antenodals still 

 greater than two. Here we refer particularly to the beautiful 

 and interesting genus Phenacolestes (fig. 164), of which two species, 

 P. mirandus Scudder, and P. parallelus Cockerell, have been 

 found, both in a very good state of preservation. One specimen 

 of the latter is almost complete, and lies with wings outspread. 

 This suggests that Phenacolestes used to rest with outspread 

 wings a habit still preserved in the allied Australian genera 

 Argiolestes and Podopteryx, but long since lost in the great majority 

 of Agrionidae. The venation is typically Megapodagrionine, except 

 for the extra antenodals, and the greater distance of the nodus 



