OF THE TABANID^E OF THE UNITED STATES. 369 



CHRYSOPS. 



The great difference in the coloring of the body, existing between the males and the fe- 

 males of Chrysops and the comparative rarity of the former in collections, compelled me to 

 adopt the plan of basing this monographic essay principally on the female specimens. Thus 

 the analytical table is drawn for females only ; in the diagnoses and descriptions, the fe- 

 males are introduced first ; short, comparative descriptions of the males are added, where- 

 ever they are known. Although it seems easy enough to refer the males to the proper 

 females, by the comparison of the design on the wings, and especiallj- on their distal por- 

 tion, which is usually identical in both se.xes, I would hesitate to place an absolute reliance 

 on such identifications, until they were confirmed by actual observation, that is, by a cap- 

 ture of both sexes together in the saaie locality. Such captures I have been able to make 

 in a very few cases only, and for this reason most of the females described below are ac- 

 companied by probable, but nevertheless hypothetical, males. 



For further details on the genus Chrysops, I refer to Dr. Loew's paper on the European 

 species (Verb. Zool. Bot. Gesellsch. 1858, p. G1.3). I would only add a single remark con- 

 cerning a character not mentioned by him, namely, the coloring of the eyes in living speci- 

 mens. All the American species of Chrysops which I had the opportunity to observe alive, 

 have the eyes colored very nearl}^ in the same manner (fig. 1); that is, the ground-color 

 being gi'een, there is along the occipital margin a dark purple Ijorder with an indentation 

 in the middle ; on the opposite or frontal margin, there are three purple spots ; and between 

 the two, in the middle of the eye, there is a fourth sj^ot, usually 

 arrow-shaped, the shaft of which reaches upwards .and ends in the 

 occipital border (C. excitans). All the species observed b}' nic 

 show only modifications of this design. Sometiuies the occipital 



border, instead of being notched, is interrupted in the middle; ,,. ,,. „ 



. . . . ' iig. 1 . I'lg. 2. l'ig-3. 



or the arrow-head is connected on one side with the middle one 

 of the three spots near the frontal margin {C. phiiujrns); or the shaft is interrupted 

 above (C. niger), or altogether wanting; in the latter case, the arrow-shaped spot is 

 sometimes replaced by a more or less I'ounded one, and when this round spot is con- 

 nected with the lateral spot near it (fig. 2, C. fag ax) the pattern appears considerably 

 modified, although it belongs to the same original type. Slight variations occur in the 

 same species, and my observations have not been sufficiently numerous to enable me to 

 characterize the eyes of each species separately. C. astiiaiis. montaniis, liUavls, excitans, 

 deUcalulus, niger, uniolttaius, j)l(ingens and fit g ax have their ej^es colored on the above 

 described pattern with the indicated modifications. The male specimens show the same 

 design, only modified by the lengthening of its upper half and the shortening of the lower 

 one, the former having the larger and the latter the smaller facets. The only excep)tional 

 pattern, which I have hitherto observed, is that of the eyes of C. flavichis Wicd, a species 

 very different in its general appearance and coloring from the typical Chrysops. (See fig. 

 3.) In this pattern the central spot (the arrow-head,) which is the most persistent feature 

 in the eyes of the first pattern, has disappeared. 



A few words onl}- will be necessary in explanation of the terms used by me in the 

 following descriptions. I call ajilcal spot every iufuscation of the portion of the wing 



MEMOIRS BOST. SOC. NAT. HIST. VOL. II. 93 



