396 C. R. OSTEN SACKEN'S PRODROME 



at base, m'ulille and liinil tibia? at base and in tlii> middle, witli a broad wliito ring; first joint of middle and 

 liind tarsi wliile, the tij) bliicl<. Al)domen witli two wbite spots on cacli segment, beginning with llie tliird 

 and witli while posterior borders, dilated in the middle. 

 Length, lU-11 mm. 



This species is almost identical with the European H. pluvialis (compare the description 

 and the figure in Meigen, Syst. Beschr., ir, p. GO, Tab. 14, f. 8-16). A constant difference 

 seems to exist in the coloring of the third joint of the anteniare, Avhicli 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 fu'st half of the third joint more or less tinged with 

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

 imens which I have for comiDarison ; the front seems bx'oader ; there is no vestige of the 

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

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

 fully carried out. However, 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. Coues) ; Southern Montana ; British Columbia (Crotch). I have compared more than 

 two dozen specimens. 



DIABASIS. 



Established by Macquart in the Suites a Bujfon and in tire Dlpttrcs Exotlques, this genus 

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

 with it, the rather low in-iertlon of the antenme, and the rather broad fore tibia;, there 

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

 of the characters mentioned hy 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, Dlahasls 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 Tabanus. 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, 

 perpendicular to the stripe, runs crosswise toward the antennaa, dividing in two the inner 

 and lower portion of the eye, which is purple. 



Diabasis ferrugata. 



Chrj/sops firriigatus Fabricius, Syst. Ant)., Ill, 2. 



Tubulins ferriir/dliis Wiedemann, Dij)t. E.xot., I, ]i. 94, 56; Auss., Zwcifl., i, p. 186, 113. 



Dichelucera ferrur/atu Walker, List, etr., i, p. 191 and v, ji. 148. 



Diabusis atceniu Alacqiiart, Dipt. Exot., i, 1, p. 15"2 and Waliier, List, etc., v, p. 271. 



Chrjsops a]>proximuns Walker, List, etc., i, p. 198. 



C'hri/sops converffcns Walker, List, etc., i, p. 198. 



Tubanus amaricunus Palisot dc Beanvois, Dipt., Tab. iii, f. 6. 



labaims Mondanii Bellardi, Saggio, etc., i, p. 68, Tab. ii, f. 11. 



