EKAX. 201 



touching the hind margin with the apex ; the sides of the segments filled by triangles of an impure, 

 silvery-white : on segments 6 and 7 the lateral margins only whitish, the middle occupied by an opaque 

 square of brownish-black ; segment 5 forms the transition in both sexes, but principally in the male ; 

 the silvery parts of segments 2-4 beset with sparse white hairs, combed outwards ; ovipositor com- 

 paratively short, equal to about two or two and a half of the preceding segments. Legs deep reddish, 

 with theusual appressed pubescence of whitish hairs, and long, soft, whitish or yellowish hairs (especially 

 in the male) and black bristles ; femora black on the underside. „Wings with a slight yellowish-brown tinge j 

 second submarginal cell distinctly appendiculate, rather long, its proximal end reaching considerably 

 beyond the proximal end of the second posterior cell ; no incrassation of the costa in the male. 

 Length, S , 23-25 millim. ; § , without ovipositor 22-23 millim., with it about 26 millim. 



Sab. Mexico, Presidio (Forrer). 



The rather unmeaning description of E. argyrogaster, Macq. (Dipt. Exot. Suppl. i. 

 p. 84, Yucatan), has something in common with the present species, especially as 

 regards the abdomen ; but the " tariere longue " does not agree at all. In my 

 'Catalogue,' 1878, p. 234, note 126, I have mentioned that E. argyrogaster, the 

 type of which I had a glimpse some years ago, has a superficial resemblance to 

 E. maculatus, E. ambiguus, &c. This is also the case with E. triton. 



5. Erax rapax, sp. n., <$ $ . 



Face and front saturate yellow-pollinose ; facial tubercle prominent, with dull yellow hairs and bristles ; palpi 

 black, with dull yellow hairs ; antennas black, the basal joints beset with short yellowish hairs ; beard 

 pale yellow, as are the other occipital hairs, except the black stiff bristles of the upper orbit ; ocellar 

 tubercle with black bristles. Thorax brownish-yellow ; dor so-central stripe dark brown, well-marked ; 

 its median line subobsolete, merely marked by a light brownish pollen; the lateral stripes or spots 

 ill-defined, shifting according to the incidence of the light ; thoracic and scutellar macrochaetae usually 

 black, but often, especially in the female, some of the macrochaetae are pale. Abdomen, male : black at the 

 base, the sides with a yellowish-grey pollen and yellowish hairs ; the distal half of the third segment, as 

 well as segments 4, 5, 6, silvery, with silvery hairs, parted in the middle and combed outwards ; segment 7 

 blackish, with white stripes at the sides and in the middle (in one of the specimens a white pollen covers 

 nearly the whole surface, very little black remaining visible) ; forceps large, black, beset with yellowish 

 and black hairs, without brush of hairs on the underside (like that of E. anomalus, E.jubatus, &c.) ; female : 

 of a uniform golden yellowish -brown, with shifting darker shadows on the sides — the shadows produced 

 by the dark brown ground-colour being modified by a short, recumbent, not very dense, golden-yellowish 

 pubescence evenly spread over the whole surface, and by a thin yellowish-grey pollen irregularly spread 

 over the central line of the back (more distinctly visible when the head of the insect is away from the light 

 than in the opposite direction) ; on each side a distinct, rather broad, dull grey stripe reaching from the first 

 to the seventh segment ; the hind margins of the same segments having a yellowish-grey border, visible in 

 a certain light only. Venter grey. Ovipositor equal in length to about three of the preceding segments. 

 Legs black ; besides the usual bristles, beset, especially on the tibiae, with soft yellow hairs, which are 

 short and more or less recumbent on the upperside and longer and erect on the underside ; the long bristles 

 on the hinder side of the tibiae of the female yellow ; the usual reddish down covering the hinder side of 

 the hind tibiae and of the corresponding metatarsus rather conspicuous. Wings with a very slight 

 yellowish-brown tinge, especially on the distal half; second submarginal cell long, its proximal end being 

 a little nearer to the anterior cross-vein than to the proximal end of the second posterior cell ; the stump 

 comparatively long ; costal margin not expanded. 



Length of the male, without the forceps, 19-21 millim. ; of the female, without the ovipositor, about 21 millim. 



Edb. Mexico, Northern Sonora {Morrison). Three males and two females. 



E. stamineus, Willist. (Montana), must be allied to this species ; but it is much 

 biol. centk.-amek., Dipt., March 1887. 2 d 



