During 1900–01 I made some studies on the Bombide occurring in Colorado. This paper is an abstract of those studies, the main body of which is in an unpublished thesis deposited with the Secretary of the State Board of Agriculture at Ft. Collins, Colorado. The material used is in the collection at the State Agricultural College of Colorado, and in my own collection; also a few specimens at the U. S. Nat. Mus. Most of the collection passed through the hands of Mr. Wm. H. Ashmead, who corrected determinations and who very kindly looked over the table given below, not only making corrections in it, but adding some species I had not recognized.