370 C. R. OSTEN SACKEN'S PRODROME 



beyond the usual crossband, -wbether this infuscation is connected with the crossband or 

 separated from it. The hyahne interval between the crossband and the apical spot, I have 

 usually called the hyaluie triumjle. 



In identifying species of Chrysops, the principal attention should be paid to the design of 

 the wings. It is characteristic of the species and, at the same time, remarkably constant 

 within the same species. It also helps to refer the male specimens to their females, however 

 different in coloring the sexes may be. The wings of the male are usually somewhat darker 

 on tlieir proximal half; the infuscation of the two basal cells reaches farther towards the 

 distal end of these cells, the anal cell and anal angle often have a brownisli tinge, which 

 may not exist in the female. But in the distal half of the wing, especiall^^ in the shape of 

 the apical spot and of the hj'aline triangle between it and the crossl:)and, the resemblance 

 between the sexes is, in most cases, much greater. The coloring of the antenna^ and of 

 the legs is very variable within the same species and in the same sex, and not to be relied 

 ui)()n. The relative extent of black and reddish on the abdomen is also very variable in 

 the same species ; often the whole appearance of a sjiecimen is changed by an extensive 

 prevalence of the one or the other color. The colorino; of the wino;s is the onlv safe ffuide 

 through all these difficulties. 



The insufficiency of most of the descriptions by Walker and Macquart has compelled me, 

 in many cases, to quote their descrijstions as doubtfid sjaionyms of my supposed new spe- 

 cies. As I give detailed and I hope sufficiently clear, descriptions of all the species, I trust 

 that in most cases there will be but little dovdjt as to the species I mean to describe. The 

 other question, that of the names to be given to these species, is comparatively of a sec- 

 ondary importance, and can be settled only through the comparison of the original types of 

 the earlier descriptions in London and Paris. 



I describe in this paper twenty-three species of Chrysops distributed over the area con- 

 tained ]:)etween the District of Columbia, Wisconsin and Canada (besides C. airojms. from 

 Florida) ; no doubt many more species will be discovered. The whole of Europe north of 

 the Alps possesses only twelve species ; the southern peninsulas have four species more ; 

 total for Europe sixteen sjiecies. Among the twentj'-four North American species here 

 described seven have no apical spot, that is the whole apical portion of the wing is h^yaline. 

 Of the sixteen European species not a single one belongs to this categ•or3^ Four European 

 species have a hyaline or subhyaline spot in the middle of the ciossband ; no such species 

 have been discovered yet in the Atlantic basin of North America ; but I have seen one or 

 two from California. Such are the results of a comparison of both foiinas, liased on the de- 

 scriptions of the European species. A comparison of specimens would j^iobabh' disclose 

 still other curious analogies or differences ; unfortunately I have specimens of only two Eu- 

 ropean species before me. 



ANALYTICAL TAliLE OP THE SPECIES (CONSTRUCTED FOR FEMALE SPECIMENS ONLy). 



I Tlie apex of tlio wiiijjf, lieyoiid tlie crossbaTul, is hyaline 2. 



' 1 The aj)c'x of tlie wing, beyond tlie crossband, is more or less iiifuscateil 8. 



r Tlie wliole wing, except the apex, is black, fading into dark -gray posteriorly . . 1. atropos n. sp. 

 1 The whole wing, besides the apex, is not black 3. 



