230 C R. Osten Sacken: Diptera 



surroxinding, but not covering, the posterior crossvein and an angular, 

 large spot in the discal and third posterior cells; the root of the wing 

 and a segment of the apex are likewise yellow; the only white mark 

 is a circular small spot in the first posterior cell, within the sinus of 



^^V 



Trypeta Alkestis. 



the third vein ; the apex of the yellow triangle above the anterior cross- 

 vein and a narrow streak across the second basal cell are also white. 

 Third antennal joint slightly excised anteriorly, rounded at the tip, 

 which does not reach the peristoma; arista rather densely plumose. 

 The chaetotaxy is the normal one of Trypeta (as far as it is preserved 

 on the specimen); thoracic bristles rather long; two praescutellar pairs 

 and two scutellar; but between the latter, a very minute third pair; the 

 praesutural bristle is present; I perceive but one lower fronto-orbital ; but 

 the head of the specimen is damaged. Length 8—9 mm. — A single male. 



NB. I. The course of the first vein in T. Alkestis is peculiar: 

 after joining the costa, it seems to continue alongside of it, thus pro- 

 ducing the appearance of a flattened thickening of the costal vein 

 between the tip of the first vein and the apex. This thickening gives 

 an unusual breadth to the apical half of the wing; it is possible that 

 it characterizes the male sex only. Something similar, although in a 

 lesser degree takes place in T. Manto. 



NB. II. T. Alkestis, in the distribution of the spots on the wings, 

 the venation, the structure of the antennae etc. has a good deal in 

 common with Themara ampla Walk. J. Pr. Lin. Soc. I, 33, Tab. 1, 

 f. 5, and may belong to the same generic group, whether this group 

 be called Themara or Acanthoneura. It must be borne in mind that 

 the specimen which Mr. Walker describes here as a male, he declares 

 1. c. p. 124 to be a female, the true male being Achias macuHpennis 

 Westw.; a fly which I believe to be a Trypetid, its Achias-like head 

 notwithstanding (Comp. my Enumer. etc. p. 73). 



Trypeta Polyxena 0. S. Enumer. 74 probably likewise belongs to 

 the same group; only the third vein is much more straight, perhaps 

 owing to its sex only, as the described specimen was a female. 



