234 DIPTERA OP NORTH AMERICA. [PART IV. 



the appearance of two joints. Eyes large, very convex, pubes- 

 cent, separated above by a very broad front ; two ocelli are 

 distinctly visible on each side of a gibbosity immediately above 

 the antennae ; the latter are considerably longer than the head 

 and the thorax taken together, setaceous, very slender, finely 

 pubescent ; first and second joints very short ; the third and the 

 following subcylindrical, elongated, gradually becoming more 

 slender ; in dry specimens the joints of the flagellum, except the 

 basal ones, are indistinct ; in living specimens, under the micro- 

 scope, the antennae appear 16-jointed. J The thoracic suture is 

 well marked ; the interval between it and the scutellum shows a 

 smooth depression, and no trace of the longitudinal furrow usu- 

 ally visible there. Feet slender, with an almost imperceptible 

 pubescence. Wings (Tab. II, fig. 13, wing of T. bimacula Walk.) 

 rather broad ; the tip of the auxiliary vein is nearly opposite the 

 tip of the fifth longitudinal vein ; the subcostal cross-vein is at a 

 distance from the tip of the auxiliary vein, which is nearly equal 

 to the breadth of the wing ; the tip of the first longitudinal vein 

 is nearly opposite the posterior branch of the first fork of the 

 fourth vein ; the second longitudinal vein originates before the 

 middle of the length of the wing ; the subcostal cross-vein is at a 

 distance beyond it, which is a little longer than the great cross- 

 vein ; the prsefurca, gently arcuated at its basis, is comparatively 

 long, but little shorter than the second submarginal cell ; the first 

 submarginal cell is shorter than the second, its petiole being 

 about equal in length to the great cross-vein ; the marginal cross- 

 vein is a little beyond the inner end of the first submarginal cell ; 

 the second submarginal and first posterior cells are of equal 

 length ; the discal cell is somewhat elongated, projecting inside 

 of the small cross-vein ; the great cross-vein is opposite the 

 further end of the discal cell ; the fifth longitudinal vein is angu- 

 larly broken at the great cross-vein ; sixth vein straight ; seventh 

 very short, arcuated, incurved to the anal angle. The forceps of 

 the male consists of the usual two subcylindrical basal pieces, 

 each of which, instead of any horny organs, bears a movable, 

 elongated, cylindrical, fleshy appendage ; these appendages, when 



1 This number has been for the first time correctly stated by Mr. West- 

 wood in the explanation to Tab. XXVI, fig. 8, of Walker's 7ns. Brit. Dipt. 

 Vol. Ill ; in former works it was given incorrectly or not mentioned at all. 



