CHARLES P. ALEXANDER 241 



and so the list of species as given below may not indicate the full 

 number of species represented. There are a large number of speci- 

 mens of a small species with uniform pleura which are possilly 

 puella Williston but I have never seen a male that answers the 

 figure given by Williston in his original characterization of the 

 form. 



The best criteria for working upon these insects are the presence 

 or absence of a stigmal spot, the length of subcosta of the wings, an 

 open or closed cell 1st M^, pleurae striped or uniform, character of 

 the genitalia of the males, such as the appendages of the pleurites, 

 the structure and length of the gonapophyses and penis guard, etc. 



The American forms may be provisionally'- divided into groups 

 of species as follows : 



1 : cinerea group with the cell 1st Mo open, due to the obliteration 

 of the outer deflection of M3; this includes cinerea Doane and 

 alexanderi Johnson. 



2: pleuralis group with the cell 1st if 2 closed, stigma distinct, 

 pleura distinctly striped; this includes pleuralis Williston, ama- 

 zona Alexander, recurvata Alexander and sacandaga Alexander. 



3 : manca group with the cell 1st M2 closed, stigma lacking. This 

 group includes a heterogeneous collection of forms such as manca 

 Osten Sacken, puella Williston, puer Alexander, calverti Alexander 

 and the new forms described below as extensa, inermis and scimitar. 

 The males known to me may be separated by the following key: 



1. Hypopysium small, tubular, the pleural pieces not distinct. (Costa 



Rica) calverti Alexander 



Hypopygium with definite cylindrical pleurites which bear more or 

 less prominent chitinized appendages 2 



2. Pleurites not armed with a chitinized appendage; guard of the penis 



long, subcosta short 3 



Pleurites armed with chitinized appendages 4 



3. Pleurites long, slender, finger-like; ventral gonapophyses consisting 



of conspicuous divergent chitinized hooks. [Small species with 

 uniform pleura.] (Eastern United States), .manca Osten Sacken 

 Pleurites shorter and stouter; ventral gonapophyse an oval lobe with 

 a few rather stout hairs. [Large species with indistinct pleural 

 stripes.] (British Guiana) inermis sp. n. 



4. Pleurites with the chitinized appendage almost straight beyond the 



base, expanded before the tip. [Pleura distinctly striped, Sc 

 long, ending slightly before the origin of /?&•.] (British Guiana) 



extensa sp. n. 



TRANS. AM. EXT. SOC, XL. 



