496 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 114 



Taxonomic Considerations 



For many years, one of the major systematic problems within the 

 Acrolophidae has been the apparent lack of generic characters. The 

 family is fairly large now and eventually, when the many undescribed 

 species existing in Mexico, Central America, and South America have 

 been accounted for, it will undoubtedly embrace some hundreds of 

 species. It is reasonable to assume that such a large assemblage of 

 species should fall naturally into a number of faiiiy distinct genera. 

 In addition, for the purely practical reasons of preparing keys and 

 separating the species, it is obvious that the worker, for his own conven- 

 ience, would very much like to subdivide this assemblage of species 

 into a series of smaller and more easily handled groups or genera. 

 Although the writer has kept these facts in mind throughout the course 

 of the present revision, he has not been able to find any positive generic 

 characters in the Acrolophidae. At best, he has been able to show the 

 existence of a nmiiber of small but distinct species groups which at 

 present may be regarded as potential genera. 



In separating a group of species into a number of genera, any one 

 genus may be based either upon a single character or upon a group of 

 characters. The Acrolophidae show an annoying resistance to both 

 these lines of approach. The compound eye serves as a good example 

 of the difficulties involved in selecting a single character for generic 

 separation: in some species the eye is entirely naked while in others 

 it is densely setose. Between these two extremes are found well- 

 defined gradations of setosity, each exhibited in a consistent manner 

 by one or more species, with the individuals of any one species having 

 exactly the same amount and type of vestiture upon the compound eye. 

 However, it is possible to take from tliese same species a series of speci- 

 mens that exhibits a very gradual and subtle transition of the com- 

 pound eye from complete nakedness to a very heavily setose condition. 

 Thus, at the generic level, this character is intergrading and must be 

 abandoned. 



Exactly the same situation occurs with the labial palpi, which on 

 many species are greatly elongated, while on others they are consid- 

 erably shortened. With the genital structures the worker fares no 

 better. The uncus is strongly bifurcate in some species while it con- 

 sists of a single, hookhke process in others; likewise, the gnathos is 

 strongly paired in some species and fused in others, but it will exhibit 

 all degrees of transition between these two extremes through a series 

 of specimens properly chosen from a number of different species. 



The venation of the wings offers neither specific nor generic charac- 

 ters. In view of the fact that the arrangement of the veins may be 

 quite dissimilar in the right and left wings of a single specimen, any 

 consideration of venation has been abandoned in the present revision. 



