Occasional Papers of the Museum of Zoology 7 



armed with two dorsal basal hooks and the dorsal apex of the 

 segment produced posteriorly in a long tapering snout; female 

 vulvar lamina %vith a broad, short base and two long tapering 

 branches which reach nearly to or slightly beyond the apex of 

 segment 9, branches apparently flexible as, in the same species, 

 they are parallel and contiguous or the apices may be separated, 

 the apex of each branch curved outAvard and away from the 

 other branch. 



With the description of A. furcatus in this paper three spe- 

 cies of Archaeogomphus are now known. The wings of a 

 male from Brazil have been figured but not named by Need- 

 ham. It is not impossible that this male is A. infans Ris 

 described from two females, the only known specimens, from 

 Argentina. The other two species, hamatns and furcatus, are 

 known from both sexes. 



The females of the three species may be separated by the 

 following brief key : 



I. Rear of occiput armed with two posteriorly directed spines or 

 horns ; two or three cells posterior to Cu^ in the hind wing which 

 do not reach the posterior wing margin furcatus 



1'. Rear of occiput not armed with posteriorly directed horns 2. 



2 (i'). One to three cells posterior to Cu2 in the hind wing which 

 do not reach the posterior wing margin hamatus 



y. Six cells posterior to Cu^ in the hind wing which do not reach the 

 posterior wing margin infans 



It is certain that the venational character of iiifaiis employed 

 above and based only on Ris's figure of one wing will prove 

 variable, but I believe the character, when the limits of varia- 

 tion have been determined, will prove sufficient for the separa- 

 tion of infa)is and hamatus. In the coalescence of the five 

 veins at the posterior angle of the triangle in the hind wing 

 of infatis and the separation of these veins into two groups, 



