AMERICAN DIPTERA. 137 



The Robber-flies of America, north of Mexico, belong- 

 ing- to the Subfamilies Leptogastrin.se 

 and Dasypogoninse. 



BY ERNEST A. BACK, PH.D. 



OF THE 



MASSACHUSETTS AGRICULTURAL COLLEGE, AMHERST, MASS. 



INTRODUCTION. 



This contribution to our knowledge of the Asilidae (Robber- 

 flies) of America, north of Mexico, is the result of several 

 years of more or less interrupted study at the Insectary of 

 the Entomological Department of the Massachusetts Agricul- 

 tural College, under the direct supervision of Doctors Charles 

 H. and Henry T. Fernald, and forms a portion of a thesis for 

 the degree of doctor of philosophy. It is an attempt to place 

 before those interested in the Asilids of our country a single 

 paper by the aid of which the identification of these interesting 

 flies may be greatly facilitated. 



The writer first became interested in the Asilidae about six 

 years ago when, on the departure of Mr. Geo. F. Babb, who 

 had been working upon this family, the work was placed in 

 his hands. Mr. Babb's original plan was a paper on the genus 

 Asilus, sensu lat., and as a foundation, he had just completed 

 the translation of the description of all the Asilidae then known 

 north of Mexico, when he was called away from the college. 

 Through the lack of time and material in Asilus, it was de- 

 cided to limit the work of Leptogastrinae and Dasypogoninae 

 of America, north of Mexico, although the unique Cuban 

 genus Sphageus and the Mexican Ar chile str is, have been in- 

 cluded. 



There are herein given the description of one hundred and 

 ninety-four species and thirty-six genera, exclusive of those 

 unrecognizable species referred by the older writers to the 

 genus Dasypogon, which will be listed at the end of the paper. 

 Of these, one genus, Willistonia, and twenty species are new. 

 So far as has been possible, the type of each genus, and the 

 location of the specific types, has been given at the end of each 



TRANS. AM. ENT. SOC, XXXV. (18) APRIL, 1909. 



