336 SUPPLEMENT. 



decisive kind : the lamellae of the hypopygium are large, dark hrown, almost square, 

 with but two or three long hairs on the outer side ; the front has much less silver dust ; 

 the thorax is of a purer green, and the abdomen runs more to violet ; the lateral crook 

 to the middle tarsi is much less pronounced, though perceptible.] 



HERCOSTOMUS. 



Hercostomus, Loew, Neue Beitr. v. p. 9 (1857). 



1. HerCOStomuS flavipes, sp. n. (Tab. VI. fig. 17, wing of 6 .) 



(5 . Face rather wide, covered with white dust ; antennae short, black, the basal oints reddish below, the third 

 large, with a point on the upper angle. Front dull green. Cilia of the inferior orbit white. Thorax 

 and abdomen moderately bright green, on the sides with whitish dust. Tegulse and halteres yellow, the 

 former with black cilia. Hypopygium bulky, dark green on the main part; the lamellae rather small, 

 almost circular, with well-defined blackish border, the hairs inconspicuous. Legs yellow : base of the 

 hind coxae and half of the middle pair infuscated ; hind tarsi infuscated from the base, the middle pair 

 from the tip of the first joint, the front pair only slightly so at the tip. Wings subhyaline ; costa not 

 thickened; fourth vein bent towards the third at the first third of the last section, thence gently converging 

 towards it. 

 Length 3 millim. 



Bab. Mexico, Omilteme and Amula in Guerrero (H. H. Smith). 



Four males ; in some of them the reddish colour is more extended on the antenna?, 

 so as to include part of the underside of the third joint. 



Two females from Tabasco, which seem to belong here, differ in having the antenna? 

 yellow, with the third joint infuscated, and the hind coxae wholly yellow. 



PELASTONEURUS. 



Pelastoneurus, Loew, Neue Beitr. viii. p. 36 (1861). 



It is almost impossible to define the genera Pelastoneurus, Paraclius, and Sarcionus 

 by any constant differences ; they may, however, be separated pretty generally by the 

 following characters : — 



Pelastoneurus has a wide face in both sexes, the lower part convex ; the arista is 

 plumose ; the last section of the fourth vein is usually convex when viewed from 

 behind. Paraclius has a bare or nearly bare arista ; a face of varying width, but never 

 very wide nor convex below; the last section of the fourth vein is usually concave 

 when viewed from behind. Sarcionus has a very narrow face, usually only a tenth 

 the width of the head ; the arista is plumose ; the last section of the fourth vein is 

 rather variable in form, in most cases intermediate in this respect between the two 

 other genera, e. g. not very convex or concave. 



Since these distinctions are in some cases difficult of application, I have thought it 

 best to give a single combined Table of the species of all three genera that are known 

 from Mexico : — 



