l6 E. B. WlLUAMSON 



In marked contrast to the dull, common-looking tenerals and females, the 

 fully adult males of peruziana are among the most brilliant and handsome 

 of dragonfllies. In flight they are swift and agile, and suggest simplicicollis, 

 but I have never observed them indulging in the complicated evolutions of 

 the latter species. 



7. Erythcmis plcbcja Burmeister. Colombia: Puerto Colombia, Decem- 

 ber 10 and II, 1916; Santa Marta, (5), December 13, 16, and 18, 1916, and 

 January 3, 1917; Don Jaca, December 17, 1916; Rio Frio, (4, 5, 6), Jan- 

 uary 4-8, 1917; Fundacion, (i, 4, 5, 6), January 13, 1917; Bolivar, (5, 6). 

 December 20, 21, 23, and 26, 1916, and January 2, 1917; Zambrano, January 

 20, 1917; El Banco, (i, 2, 4, 5, 6), January 23, 1917; Gamarra, January 27, 

 1917. Venezuela: Tucacas, (2, 5, 6), March 23, 25, 1920; Palma Sola, (i, 

 5, 6), March 8 and 10, 1920; Bejuma, (6), February 13, 18, and 24, 1920; 

 Encontrados. (i, 5, 6), April 25, 1920; El Guayabo, (4, 5, 6), April 20, 1920. 



A male of this species, collected in Jamaica and received from Carpenter, 

 is labelled Jiacmatogastra, but I do not think this mistake is likely to be fre- 

 quent as, if any confusion occurs as regards plebeja, it is likely to be with 

 attala; and as Calvert has pointed out, the adult male of Jiaenmtogastra super- 

 'ficially resembles the adult male, not of another Erythemis, but a species of 

 another genus, Rhodopygia hollandi, just as another Erythemis, peruviana, 

 superficially resembles Planiplax sanguiniventris rather than some other spe- 

 cies of Erythemis. 



Bates, as recorded by Ris, states of plebeja: "Banks of the river Tapajos 

 near Santarem. settling on bushes in the woods." It is an agile species and 

 is found widely scattered in practically all the environments of any locality 

 where it occurs. 



Conclusions 



Finally, I should like to call attention to the present status 

 of Erythemis and a very different genus of American dragonflies, Hetaerina, 

 and to certain facts in their life histories, leaving to other students any con- 

 clusions as to the significance of these facts in explaining present conditions. 

 There are nine known species of Erythemis as against about fifty species of 

 Hetaerina. And yet, in any locality (an area three to ten miles in diameter) 

 the largest known list of Hetaerinas is four species, or eight per cent of the 

 total, while in Erythemis the largest local list is six species, or sixty-six and 

 two-thirds per cent of the total. Moreover, in any locality the species of 

 Erythemis there tend to more fully occupy the various environments of the 

 locality than do Hetaerinas, or one environment in the locality may harbor 

 all the Erythemis found there, while these conditions are usually reversed in 

 Hetaerinas, each species often showing a marked preference for a certain 

 ecological habitat. 



The species of Erythemis, as larvae, live in stagnant water, and Hetae- 

 rinas live in running water. Streams offer a greater variety of ecological 

 conditions than fresh-water ponds offer. 



Hetaerinas as imagoes are closely bound to the streams which make their 

 larval home. Their dispersal to new habitats is doubtless rare and accidental. 



