Sors, McAlpine, 2007

McAlpine, D. K., 2007, New Taxa of Signal Flies (Diptera: Platystomatidae) of New Caledonia, Records of the Australian Museum 59 (1), pp. 65-77 : 73

Sors n.gen.

Type species Sors wrightae n.sp.

Description. Female (male unknown). Small, stout, dark flies; cuticle of head, thorax, and abdomen almost entirely pruinescent and non-shining; wing heavily variegated.

Head anteroposteriorly compressed; vertical carina moderately sharp; face without prominent median carina; lower part of occiput convex, c. upper third flat to slightly concave; eye without obvious ommatrichia; the following bristles well developed: inner and outer vertical, upper fronto-orbital, postgenal; ocellar bristles small, hair-like, pale, widely divergent; postvertical bristles small, subparallel or divergent, procurved, inserted well below vertical carina. Antenna moderately short and stout; arista with segment 6 irregularly pubescent on whole length. Prelabrum well developed, broad but shallow; palpus moderately broad.

Thorax. Cuticle with general covering of dense, short, dark microtrichia (typical pruinescence), but with pale markings indicated by distinctly longer, whitish microtrichia standing out in relief; mesoscutum much broader than long, extensively setulose; scutellum broadly rounded in dorsal view, slightly convex dorsally, with thin but not sharp posterior margin, extensively setulose, with sockets of posterior bristles prominent, tilted upwards so that rims form horizontal circles; mesopleuron only slightly convex; the following thoracic bristles present: humeral, 1 + 1 notopleurals, supra-alar, postalar, posterior intra-alar, one dorsocentral, prescutellar acrostichal, three pairs of scutellars, mesopleural; sternopleural bristle absent. Legs moderately short and stout; fore femur with posterodorsal and posteroventral bristles; mid tibia with one large apical ventral spur and no distinct secondary spurs. Wing rather broad; subcosta gradually approaching costa distally; vein 1 with a rather dense dorsal series of setulae from just beyond level of humeral crossvein, without more basal setulae; vein 2 without kink near mid-length; veins 3 and 4 very slightly divergent distally; vein 3 with numerous dorsal setulae; anterior crossvein as long as penultimate section of vein 4 or almost so; discal cell broad, relative to that of Platystoma and Euprosopia ; anal cell obtusely angular posterodistally; squama forming moderately short rounded lobe.

Abdomen. Tergite 5 moderately large; ovipositor sheath short and broad; aculeus slender.

Distribution New Caledonia: only known from southern part of Grande Terre.

Notes

Sors resembles Euthyplatystoma Hendel (Oriental) and Platystoma Meigen (Palaearctic) . The anteroposteriorly compressed head, slightly but broadly swollen on lower occipital surface, with eye-surface broad, little convex and largely directed forwards, so that the eye appears narrow in profile, is typical of both these genera. The general dense covering of pruinescence on the mosopleuron and some other parts of the thorax is short and dark, but the whitish flecks are the effect of small zones of significantly longer white microtrichia. This condition agrees with Euthyplatystoma and Platystoma , and is not present in Euprosopia Macquart , an Australasian genus of somewhat similar general coloration though not closely related to the other genera mentioned. The relatively short, ovate antennal segment 3 also agrees with these two northern genera, rather than with a majority of Australasian platystomatine genera.

Sors differs from both Euthyplatystoma and Platystoma in having the anterior crossvein almost as long as the penultimate section of vein 4 (instead of no more than half as long), in having the section of vein 5 on discal cell arched at most only on its basal half (instead of strongly arched for all or most of its length), in having the length of the discal cell (measured along vein 4) c. 2.2× as great as maximum width (instead of more than 3× as long as wide), and in having the prelabrum markedly shallower. In Sors the single stout apical ventral spur of the mid tibia disagrees with the condition in Platystoma (five available species), which has one or more secondary spurs, but is more like that of Euthyplatystoma . It further differs from Euthyplatystoma in its much shorter, broader fore coxa, and in having the posterior margin of the scutellum quite thin, instead of thick and rounded.

In the key to genera of Lamprogastrina and Platystomina by Hendel (1914b), Sors runs to Platystoma , providing that one knows enough of the keyed genera not to be side-tracked at couplets 10 or 19. There is some difficulty at couplet 10, where, on wing venation, it could tend towards the African Sphenoprosopa Loew , but it disagrees in head structure and wing pattern (see Hendel 1914a, fig. 271). At couplet 19, Sors may be associated through couplet 20 (instead of the more appropriate couplet 24) with 5 genera belonging to the subfamily Scholastinae , on account of having the mesoscutum much broader than long. In contrast to these genera, Sors has a large female tergite 5, no strong gibbosity on the upper part of the mesopleuron, and a much more restricted geno-parafacial area.

The generic name is a Latin noun, sors (genitive sortis) meaning (among other things) a kind or sort, and is feminine.