REHN AND HEBARD 39 



robust; another of the attenuation of the distal (distad of tooth) 

 portion alone; a tendency to curve inward instead of remaining 

 straight, which may involve the whole cercus or but the distal 

 portion, and, faintest of all, a fluctuation in the curvature of the 

 tooth. These features are Hable to occur within specific limits, 

 where we ha\e sufficient material to permit us to speak with 

 authority, except in A. cjibbosns, which, while having the most 

 complex cercus, is very fixed in these characters. The sub- 

 genital plate of the male has a very great amount of individual 

 variability in the character of its distal margin, which ranges in 

 a number of species from subtruncate to rectangulate and even 

 acute-angulate. In one species {americanus) it is, however, 

 invariably fissate. 



Morphological Notes on Female Genitalia. — ^The disto-dorsal 

 abdominal segment and supra-anal plate have been discussed 

 above under the male genitalia. The cerci of the female are 

 simple, tapering and without differential characters. The ovipos- 

 itor shows variation along three lines: first, in relative length, 

 secondly, in general straightness or curvature and in straightness 

 or curvature of the ventral margin, and, lastly, in the position 

 of the apex. In the matter of relative length, we find the varia- 

 tion exhibited is largely individual or possibly environmental, 

 but not distinctly geographic. In several forms which have a 

 faint decurvature of the whole ovipositor we find individuals 

 which have the same straight (pachymerus and davisi), and this 

 is probably (pachymerus) or certainly (davisi) geographic in 

 character. The curvature or straightness of the ventral margin 

 of the ovipositor is, of course, correlated with the general form, 

 but to a slightly greater degree than the dorsal margin. The 

 immediate apex of the ovipositor may be nearly median in posi- 

 tion, but is generally ventral, the case in which it is median being 

 geographic (northern specimens of davisi) and passing into the 

 more normal type. The relative depth of the ovipositor varies 

 somewhat, but this is chiefly in davisi and is there geographic. 

 The form of the subgenital plate of the female is one of the most 

 constant diagnostic characters found in the genus; this is always 

 emarginate and ranges from subrectangulate and U-emarginate 

 to V-emarginate, or subfissate {americanus) and divided well 



TRANS. AM. ENT. SOC, XLII. 



