Silba abstata

,4 medium-sized species, about as large as S. aristella (Beck.) and S. adipata n.sp., with black tarsi and white calyptrae. The male frons relatively narrower than in most species, and broadened both above and below the mid-section. One of the oral setulae vibrissa-like. The body colour the usual greasy blue-black, but the wing distinctly yellowish-brown fumose anteriorly and at the base in mature specimens. The female ovipositor wider than in any known species of the genus with the possible exception of S. admirabilis n.sp. Male.-Head about five-sevenths as high as wide. Frons relatively narrower than usual in the family; at the narrowest point about one-sixth head width (13.0: 2.2) and about three-fifths as wide as high (2.2: 3.75); somewhat hour- glass-shaped, the narrowest point being slightly below the middle; dull black in colour but not appearing pollinose in most lights; from 16 to I8 inferior orbital setulae present on each side; genovertical plates bare and polished blue-black above the orbital bristle; in side view, no setulae visible immediately above the orbital bristles. Immediately below the ocellar plate a rather distinctive, longitudinal, dimple-like depression. Parafacials linear. One of the oral setulae strongly vibrissa-like, i.e., longer and stronger than the others in the series, with three or four smaller setulae above it in a uniserial row. Lunule silvery pollinose with 12 relatively strong setulae. Second antennal segment entirely reddish- brown, and the third narrowly reddish-brown at the base, inside; third antennal segment about 2% times as long as wide. Plumosity of arista about as wide as the width of the third antennal segment, stronthe middle to the apex, and bearing the usual number of plumules (about 17) above and below. Each palpus with a rather strong, outwardly directed bristle at the apex. Mesonotum mostly shining blue-black, but entirely cinereous pollinose posteriorly from the area immediately in front of the mesonotal macrochaetae; this pollen continuing posteriorly over the entire scutelluni. Scutellum with four or five lateral setulae on each side, and a pair of apical setulae between the apical bristles. Mesopleuron anteriorly with t~ro strong anterodorsal bristles, with a weak one both above and below them, and posteriorly with three strong posterior mesopleural bristles. Sternopleuron with nvo bristles, the anterior one ~veaker; no setulae present behind the strong sternopleural bristles. Meso- pleuron and stemopleuron uniformly, lightly pollinose. Prosternum with five or six fine I~airs on each side anteriorly. Legs and tarsi black; mid and hind tibiae each with a distinct preapical dorsal bristle, the one on the midtibia at least as long as the width of the tibia. Midtibia with a relatively very strong ventral bristle at the apex, i.e., as long as the greatest diameter of the midfemur. Wings distinctly yellowish-brown fumose anteriorly and at the bases in mature specimens, but this character less distinct in teneral, reared specimens. Calyptrae and their fringes white to pale yellowish-white. Disc of the abdomen entirely lightly cinereous pollinose from an anterior view, but subshining blue-black from other angles, the most heavily pollinose area being the disc of the second tergum.

Male genitalia as shown in Figs. 4 and 5. Female.-Agreeing with the male except for the following sexual differences: Frons relatively narrow, distinctly less than one-fourth as wide as head (2.5: 11.0) at the narrowest point; about 1 Z/S as long as wide (3.4: 2.5); anteriorlv with two distinct. converging grooves in the allotvpe, but these probably less pronounced in fullv manlred specimens. The ovipositor (Fig. 6) verv distinctive, being relatirelv o;'r~ broad for this genus, at its widest point djs6nctly wider than the distance he~wecn the apical scutellar bristles (1.45: 1.3) (Fig. 7).

Holotype, 8 , and nllotype, 9 .-Roy. Botanic. Gdns., Paradeniya, Ceylon, Aug., 1903, E. E. Green, 1903-241, bred from rotting stumps of young shoots of Dendrocalamus gigmtezrs; in the British hluseum (Natural History). Puatype.- 8, Ammati, S. Coorg., India, 3100f, Oct., 1952, P. S. Nathan, type number 6272 in the Canadian National Collection.

In Bezzi's (1920) key to the Indo-Australian species. nhstntn runs to hi.~~lcmn Bezzi but differs from that species as follows: ~Vlale frons not nearly twice as long as wide; wings not "deep yellow" and ovipositor abnormally wide as against a normal narrow one in bisulcata. Absrnta mav easily be confused with calzva Bezzi; in the former however, the plurnosity 6f the arista is distinctly longer and the frons narrower; abstata has two, only, strong anterodorsal mesopleurals with a weak one below and several setulae above thcm, whereas cnlva has three anterodorsal bristles with one weak setula above them and one below. In abstata there are, at most, five lateral scutellar setulae, whereas in calva there are about seven longer and stronger ones. In each species the male genitalia and the female ovipositors are very different (Figs. 4-7, 54-55); the ovipositor of calva is narrow as usual in this genus.