CHAKLES P. VLKXANDKU 241 



and so the list of species as Riven below may not iiulicatc the full 

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

 mens of a small species with uniform pleura which are possil ly 

 puclla 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 Ut 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 gonapoph3-ses and penis guard, etc. 



The American forms may be provisional!}- divided into groups 

 of species as follows: 



1 : cinerea group with the cell Isl Mn open, due to the obliteration 

 of the outer deflection of M^; this includes cinerea Doane and 

 alexanderi Johnson. 



2: pleuralis group with the cell 1st M2 closed, stipma distmct, 

 pleura distinctly striped; this includes pleuralis Williston, ama- 

 zona Alexander, recurvala Alexander and sacandaga Alexander. 



3: manca group with the cell /si M2 closed, stigma lacking. .This 

 group includes a heterogeneous collection of forms such as manca 

 Osten Sacken, piiella 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. Hypopygium 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 OstenSacken 



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, e.xpanded before the tip. [Pleura distinctly striped, Sr 

 long, ending slightly before the origin of Rs.] (British Guiana) 



extensa sp. n. 



TRANS. AM. E.NT. SOC., XL. 



