REHN AND HEBARD 



367 



The species at present under consideration are naturally grouped 

 as follows: 



cxiliscanorus 



■ ncbrascensis 



-mclanorJdnus 



-lyristes 



c nsujcr 



-robuslus rohustus 



rohustus crepitans 



ccmdelUanus 



velox 



-palustris 



-retusiis 



iriops 



Morphological Notes.- — -Degree of robustness is frequently of 

 value in distinguishing certain species when the sum total of 

 characters are considered. A certain amount of individual varia- 

 tion is often found in the shape of the vertex; in species having it 

 produced, the female sex has the apex averaging slightly more 

 acuminate. In species having the ventral surface of the vertex 

 marked, the maculation varies individually in intensit}^ in some 

 few specimens of every large series, and in specimens in which the 

 coloration is weak, the area covered by the same is alwaj^s cor- 

 respondingly reduced, this reduction being always greater proxi- 

 mad than distad. Thus, in species having the entire ventral 

 surface of the vertex black, among specimens of the palest colora- 

 tion exceptions occur in which this marking is less extensive, 

 reaching only to the base of, and not including, the proximal tooth. 

 In females the pronotum averages proportionately less ample, 

 the tegmina and wings are more elongate and attenuate, than 



TRAXS. AM. ENT. SOC, XL. 



