INTRODUCTION 5 



by Miss Louise Russell; comparisons with and notes on the types in 

 London and Oxford were made by Mr. I. H. H. Yarrow; Dr. H. E. 

 Evans sent a copy of his notes on the Provancher types; and Mr. 

 K. V. Krombein sent notes on the Provancher types taken in 1953. 

 Assistance from these persons and from the curators of institutions 

 and museums at Washington, Philadelphia, Cambridge, Ithaca, 

 Raleigh, Lawrence, and San Francisco, who made the types under 

 their care available for study, has permitted the kind of nomencla- 

 torial work that was sorely needed in this group. Their help is 

 gratefully acknowledged. 



Many of Banks' new species were described from a syntype series, 

 without designation of an individual type. Often the number of 

 specimens involved and sometimes even the sex is not stated. For 

 nomenclatorial purposes I have designated a lectotype in the specific 

 synonymy wherever one of Banks' new names was based on more 

 than one specimen without designation of the single type. The 

 specimen so designated is usually the one of the series labeled "type" 

 by Banks, though heretofore not designated as such in a publication. 



To my wife goes special acknowledgement for the many ways in 

 which she assisted with this study, particularly in recording distri- 

 butional data and preparing the maps. The maps are intended to 

 give a quick comprehension of the known distribution, with a spot 

 for each definite locality. Indefinite localities, hke a state, or locali- 

 ties not in the atlases at hand, could not of course be indicated by 

 definite spots and so had to be omitted. They are included, however, 

 in the lists of specimens studied. 



Tenninology 



The Rohwer and Gahan (1915, Proc. Ent. Soc. Washington, vol. 

 18, pp. 20-76) system of wing vein and ceU terminology is used. 

 This terminology is explained in figure l,a. The subgenital plate is 

 the last visible sternite — the apparent seventh but actual eighth (or 

 the morphological ninth) abdominal sternite in the male, and the 

 sixth abdominal sternite in the female. The squama, or paramere, 

 of the male genitalia is the lateral distal piece, usually the largest, 

 most lateral, most projecting, and most conspicuous paired part of 

 the external genitalia. 



An abihty to distinguish between males and females is presupposed 

 in the keys and descriptions. Males have thirteen segments in the 

 antenna (or only twelve in Pepsis formosa), seven visible abdominal 

 sternites, no sting, and a more slender build. Females have twelve 

 segments in the antenna, six visible abdominal sternites, a sting that 

 may frequently be seen exserted, a more robust build, and many 

 minor differences from the males in proportions and in the vestiture 

 and bristles. 



