20 DIPTEKA. 



base a white space about a millimetre broad ; tarsi white, distinctly longer than the 

 femora and tibiae together, very slender, whip-lash-shaped. Halteres with a brownish 

 knob. Abdomen brown ; male forceps, and the venter, brownish-yellow ; hind margins 

 of the segments with a narrow brown border. Wings with a uniform pale brownish 

 tinge ; stigma slightly darker. 



Inhabits the humid forest region (Champion). 



Fam. RHYPHID-E. 



OLBIOGASTER, gen. nov. 



Head of about the same breadth, as the thorax, rather closely applied to the latter, as there is very little 

 development of the occiput behind the eyes, and but little more behind the vertex ; the side view of the 

 head is like that of Lobogaster (Philippi, Verh. z.-b. Ges. Wien, xv. t. 24. fig. 16a), and very different 

 from that of Khyphus, where the back part of the head is very much developed. Front moderately broad ; 

 above the antennae its breadth is in both sexes a little less than the horizontal diameter of the eye about 

 the middle ; three distinct ocelli on the vertex. There is no rostral prolongation of the head whatever, so 

 that the palpi are in contact with the lower orbit of the eyes, and the rather large labellae are immediately 

 under the palpi. Palpi short, the second joint stout, the last two joints smaller. Face very little convex, 

 with some scattered hairs, (Rhyphus also has the oral opening almost immediately adjoining the lower 

 orbit of the eyes, but the structure of the mouth-parts is different ; there is a short, projecting proboscis, 

 at the end of which the labellae are much smaller than in Olbiogaster ; the second joint of the palpi is 

 likewise incrassate, but the last joint is longer). 

 Antenna} filiform ; bent backwards they would nearly reach the middle of the second abdominal segment ; 

 clothed with a dense microscopic pubescence, which, together with the cylindrical shape of the joints, 

 renders the discrimination of the latter somewhat difficult ; the joints are 16 in number, and differ but 

 little in length, except the first, which is short, subglobose, and the second, which is very short, disciform. 

 (The antennae of Rhyphus are comparatively shorter, more distinctly attenuate towards the tip, the joints 

 more distinct ; joints 1 and 2 of nearly equal length, &c.) 

 Thorax comparatively small and little convex, with a scattered, moderately long pubescence on the mesonotum ; 

 no macrochetse ; scutellum and metanotum as in Rhyphus ; the former is beset with delicate hairs, but 

 has no conspicuous pair of bristles. (Rhyphus has the more gibbose mesonotum beset with two regular 

 rows of bristles, besides other bristles, inserted above the root of the wings, on the very developed, ridge- 

 like postalar callosity, and has also a pair of bristles on the scutellum.) 

 Abdomen comparatively long and flat, almost ribbon-shaped in the male, slightly attenuate at the base and 

 a little expanded posteriorly in the female ; with seven segments (besides the genitals), not differing much 

 in length, except the seventh, which is a little shorter ; the posterior margins of segments 4, 5, 6 project 

 on the sides, being broader than the anterior margin of the next following segment. The male genitals 

 are represented by a pair of subtriangular, elongated lamels, between which a pair of pointed (horny ?) 

 organs is perceptible ; the female likewise has a pair of triangular lamels, but smaller ; I cannot perceive 

 the horny points. 

 Legs of moderate length and strength ; tibiae beset with scattered, very minute spines ; front tibiae with a single 



spur, the other pairs with two ; there is a broad, short empodium. 

 Wings elongated, moderately broad ; venation like that of Rhyphus, with this difference, that the second vein 

 converges towards the first, and reaches the costa at the same point with it (the same as in Lobogaster) ; 

 while in Rhyphus the second vein, before reaching the costa, forms a curve, diverging from the first, so 

 that the marginal cell is broader in its distal than in its proximal portion. The fifth vein, towards its 

 end, forms the same peculiar curve as in Rhyphus or Lobogaster, although in a less marked degree. (The 

 pubescence which covers the surface of the wing in Rhyphus is microscopic here, and invisible even under 

 a strong lens, except in the shape of black dots.) 



This interesting genus forms the passage between Rhyphus and the Chilian genus 



