MORGAN HEBARD 



ancestor probably having been an insect with fully developed 

 organs of flight in both sexes. ^"^ The species are each distinctive 

 to a degree in some feature; so striking is this that logical division 

 of the genus into groups is out of the question. 



The following diagram best indicates the relationship and proper 

 position of the species. 



— bolliana 



desertae 



■ americayia 



zebra 



virgimca 

 uhleriana 



fidvescens 



caiidelli 



not ha 



-lata 



dknsa 



pensylvanica 



As indicated above, greatest probable divergence from the com- 

 mon ancestor is shown by the female tegminal reduction in bolli- 

 ana and americana, least differentiation in this respect in caiidelli. 

 The character of the median and first dorsal abdominal segments 

 in the male, we believe, affords the best guide to determine the 

 specific relationships. It is of further interest to note that the 

 general character of the male supra-anal plate is the same in bolli- 

 ana, desertae and virginica; m americana and notha; in zebra, uhleri- 

 ana^'^'', fidvescens, caudelli and lata, and in divisa and pensylvanica. 



i"^ See page lo. 



^"" In this species, showing a certain degree of divergence toward the tyi)c found in 

 americana and notha. 



MEM. AM. ENT. SOC, 2. 



