342 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii6 



through the East to study types at several institutions (1958), and to 

 study types in European institutions (1959). Financial assistance 

 from both sources has made it possible to secure secretarial aid, 

 laboratory help, and illustrative assistance. 



Over the years many individuals have assisted in maldng these 

 studies possible. While it would be impracticable to name all who 

 have contributed, a few should be indicated. The most outstanding 

 has been Dr. Karl V. Ej-ombein of the United States Department of 

 Agriculture. Over many years he has been the writer's principal 

 advisor; fiu-ther, he has contributed much original information through 

 his many field studies; and finally, he has freely devoted much of his 

 time to checking the present manuscript with special attention to 

 the keys. Without his devoted help it is doubtful if this paper 

 could have been completed. Among the technical assistants who have 

 given noteworthy assistance, four deserve special mention: Marybeth 

 Buddenhagen, Helen Dickason, and Margaret Johnson, who helped 

 in checking records and references as well as many other details 

 associated with such an undertaking, and Margaret Hsieh, who is 

 responsible for most of the illustrations. The writer also is deeply 

 indebted to Dr. Paul O. Ritcher, Head of the Entomology Department, 

 Oregon State University, for the use of facilities to continue these 

 studies after retu*ement. Sincere appreciation is here expressed to my 

 wife, Johanne, for many hours of assistance in proof reading. 



Key to the Species of Cerceris 



FEMALES 



1. Stigma dark amber or black; mesosternal process usually present; species 



mostly small Group I 



Stigma light amber; mesosternal process absent; species mostly medium to 

 large 2 



2. Clypeus without a distinct medial elevation or process on the surface of the 



medial lobe; a pair of small tuberculi (sometimes very indistinct) on the 

 surface of the medial clypeal lobe just above the border; entire border 



of the clypeus without denticles Group II 



Clypeus with a distinct medial elevated process (sometimes little more than 

 a ridge but not just a convex area) on the medial lobe; distinct extensions 

 or denticle-like processes on the clypeal free border 3 



3. Clypeal process with a lamella or lamellae on the free border . . Group III 

 Clypeal process without a lamella or lamellae on the free border .... 4 



4. Pygidium not narrowing to an acute or near-acute base (sides may converge 



slightly basally) 5 



Pygidium narrowing basally to an acute or very narrow end 36 



5. Elevation on the medial lobe of the clypeus is cone shaped or with the distal 



end very much narrowed and without a distinct overhang 6 



Elevation on the medial lobe of the clypeus with a definite overhang; the 

 sides of the process may diverge, converge, or be subparallel 7 



