396 C. R. OSTEN SACK EN'S PRODROME 



at base, middle and liiiid tihiic at base and in tin; iniddlo, with a broad white ring; first joint of middle and 

 hind tarsi wliite, the tip black. Abdomen with two white spots on each segment, beginning with the third 

 and with white |)Osterior borders, dilated in the nii<ldle. 

 Length, lU-11 mm. 



This species is almost identical with the European II. jiluvkdis (compare the description 

 and the figure in Meigen, Syst. Beschr., ii, p. 60, Tab. 14, f. 8-16). A constant diflerence 

 seems to exist in the coloring of the third joint of the antennce, which is altogether black, 

 except a slight vestige, often invisible, of a paler coloring at the base of the third joint, 

 while the European specimens have the first half of the third joint more or less tinged with 

 reddish. Tlie first antennal joint in all my specimens is stouter than in the European spec- 

 imens which I have for comparison ; the front seems broader ; there is no vestige of the 

 longitudinal Avhite line along the middle of the abdomen, which usually exists in European 

 specimens ; the white picture of the wings seems to be more marked and the design more 

 fully carried out. Ilo^vever, in Europe this species is very variable and I have only a few 

 European specimens for comparison. 



Fort Resolution, Huds. B. Terr. (R. Kennicott) ; Lake Superior (A. Agassiz) ; Dacota 

 (Dr. Cones); Southern Montana ; British Columbia (Crotch). I have compared more than 

 two dozen specimens. 



DIABASIS. 



Established by Macquart in the Suites a Buffon and in the Dlpteres Exotlques, this genus 

 does not seem to be sufficiently defined ; except the shortness of the fiice, in connection 

 with it, the rather low insertion of the antennfe, and the rather broad fore tibiae, there 

 seems to exist no appreciable character to distinguish it from Tabanus. It may be that some 

 of the characters mentioned Ijy Macquart (for instance the callosities on the face) occur in 

 the other species which he places in the genus, but they do not exist in the only known 

 North American species. 



As it is, Dlabasis ferrugata, besides its general appearance and coloring, which are not 

 Tabanus-like, has only the coloration of its eyes to show, as a distinctive character. The 

 direction of the stripes of the eye is very oblique, almost from top to bottom, instead 

 of nearly horizontal, as in Taljanus. A purple stripe runs, between two green ones, from 

 the vertex downward, across the eye ; from the inner one of the green stripes, a green band, 

 perpeirdicular to the stripe, runs crosswise toward the antenncc, dividing in two the inner 

 and lower portion of the eye, which is purple. 



Diabasis fermgata. 



Chrijsops ferrntjatus Faliricins, Syst. Antl., Ill, 2. 



Tahanus ferrufjatiis Wiedemann, iJipt. Exot., I, ]). 94, 5G; Aiiss., Zwcifl., i, p. 186, 113. 



Dichelacera fermgata Walker, List, etc., i, ]). 191 and v, p. 148. 



Diabasis atcenia Macquart, Di])t. Exot., i, 1, p. 152 and AValkcr, List, etc., v, p. 271. 



Chryso2)S apjiroximans Walker, List, etc., i, p. 198. 



Chrysops convergens Walker, List, etc., i, p. 108. 



Tahanus americamis Palisot do Beanvois, Dipt., Tab. in, f. 6. 



lahanus Hondanii Bellardi, Saggio, etc., i, p. G8, Tab. u, f. 11. 



