228 PROCEEDINGS OF THE NATIONAL MUSEUM vol. m 



we find there are now 88 world species and subspecies. Thus, the 

 total number of known forms is increased by 16 percent. 



The accumulation and study of some 2,500 specimens of this rela- 

 tively rare genus revealed that in order for the author systematically 

 to treat this large number of species, two new subgenera and six 

 species groups had to be delimited. Besides using conventional 

 morphological features to distinguish species, an attempt was made to 

 use both wing venation and male genitalia. Both were found to be 

 very useful. 



A discussion of geographical distribution, phylogenj^, and biology 

 was prepared to understand more fully the relationships of this 

 cosmopolitan but rather homogeneous group of parasitic flies. 



Acknowledgments 



Without the help of numerous persons a study of this sort would 

 have been difficult, if possible at all. I especially want to extend my 

 sincere appreciation to Mr. Curtis W. Sabrosky of the U.S. Depart- 

 ment of Agriculture, Washington, D.C., for his constant help and 

 advice on the many problems of this project; Dr. Richard M. Bohart 

 of the University of California, Davis, for his inspiration and advice 

 and for reviewing the manuscript; and Dr. Willis J. Gertsch of the 

 American Museum of Natural History, New York, for determining 

 the host spiders of these flies. 



Appreciation is expressed to the many persons who have aided in 

 the collection of the acrocerids and to the following people and insti- 

 tutions for the loan of the important collections on which this study 

 was based. (The abbreviations in the following list are used through- 

 out the text to denote the location of specimens studied.) 



ALM: A. L. Melander collection, Riverside, Calif. (A. L. Melander). 



AMNH: American Museum of Natural History, New York, N.Y. (M. A. 



Cazier and C. H. Curran). 

 BMNH: British Museum of Natural History, London, England (H. Oldroyd). 

 BYU: Brigham Young University, Provo, Utah (V. M. Tanner). 



CAES: Connecticut Agricultural Experiment Station, New Haven, Conn., 



(C. L. Remington). 

 CAM: Colorado Agricultural and Mechanical College, Fort Collins, Colo. 



(T. O. Thatcher). 

 CAS: California Academy of Sciences, San Francisco, Calif. (E. L. Kessel 



and E. S. Ross). 

 CDM: C. D. MacNeill collection, Berkeley, Calif. (C. D. MacNeill). 

 CHM: C. H. Martin collection, Corvallis, Oreg. (C. H. Martin). 

 CI: Commonwealth Institute of Entomology, London, England (F. I. 



van Emden). 

 CIS: California Insect Survey Collection, University of California, 



Berkeley, Calif. (P. D. Hurd, Jr.). 

 CM: Carnegie Museum, Pittsburgh, Pa. (G. Wallace). 



