The Genus Perilestes 5 



or more specimens seen by De Selys are really conspecific, though females 

 in this genus are not readily recognized. But it happens that coniutus 

 belongs to one group in the genus while the remaining four Amazonian 

 species belong to another group, and these groups are venationally dis- 

 tinct. De Selys calls attention to this character in the male, and almost 

 certainly recognized it in the female. Of the latter sex he probably had 

 more than one specimen, as he gives two measurements for the female 

 abdomen, but the text, excepting the localities, implies a single specimen 

 of each sex. 



Immediately following the description of cornutus De Selys describes 

 attenuata (attenuatus) , apparently from a single female collected by 

 Bates at Santarem. The description is so complete that we are able to 

 almost certainly identify one of the four Amazonian species of the group 

 to which attenuatus certainly belongs as that species. 



Calvert in the B. C. A. doubtfully refers a single immature male from 

 Costa Rica to fragilis. This is a specimen of remotus described in this 

 paper. In the Odonata of the Neotropical Region he discusses two males 

 and two females from Chapada, Brazil, and summarizes in a tabulation 

 the characters of these specimens, of cornutus from De Selys' descrip- 

 tion, and of the Costa Rican male, but because of the inadequacy of the 

 earlier descriptions he was unable to certainly identify the Chapada speci- 

 mens which were referred doubtfully to fragilis. We have examined these 

 specimens, through the kindness of Mr. Kahl, and they are discussed below 

 under the name solutus. 



Relationships within the Genus and Geographical Distribution 



Species of Perilestes are found from Costa Rica in the- north to Rio 

 Janeiro, Brazil, in the south, approximately between parallels 10° north 

 and 25° south. In South America at least, they are confined to the Atlantic 

 drainage. The genus probably had its origin in the Brazilian highlands. 

 Two well defined groups, as indicated in the synoptic key to groups and 

 species, exist in the genus. Group I of this key is northern. Group II 

 southern. The northern extension of Group I may indicate that this 

 group originated during the time of and on the front ranks of the- in- 

 vasion of the present Amazonian valley. 



The northern Group I of four species has only one species in the 

 Amazonian basin. Cornutus, while clearly a member of Group I, is very 

 distinct from the remaining three species of the group. It has been taken 

 on the upper Amazon and on the Madeira River and is thus widely sep- 

 arated geographically from the nearest member of the same group, guian- 

 ensis, known certainly only from French Guiana and doubtfully from 

 British Guiana. The two remaining species of the group, magdalenae and 

 remotus, occur in the lower Magdalena Valley in Colombia, and remotus, 

 like several other northern Colombian dragonflies, is found also in Central 

 America, in this particular case in Panama and Costa Rica. It seems 

 clear that Group I has penetrated to the north over two routes, one by 



