13. DIOCTRIA 745 



though any union of the two would necessitate the use of the older name Z>. 

 hyalipennis. A specimen from the Westwood collection which is now included in 

 the Hope Museum at Oxford is labelled "■lateralis." Hylvicola informis of Moses 

 Harris in Expos. Brit. Ins., T. xlviii., f. 3 (1782) is probably this species but the 

 figure and description make any identification far from certain. 



6. D. linearis Meigen. Thorax black with brilliantly shining stripes. 

 Legs including coxae and tarsi mainly yellow. 



The smallest and slenderest British species, easily known 

 by the diagnostic characters. (Fig. 369.) 



c?. Black, mainly brilliantly shining. Face all covered with dense silvery white 

 tomentum which may bear a trace of yellow on at least the upper part, but 

 with a shining black small middle patch (scarcely one-third the width of the 

 face) just under the antennae, though the tomentum when seen from below is 

 velvety brown ; face scarcely produced even at the upper mouth-edge but 

 with a gently rounded prominence on which is placed the face-beard, which 

 forms a clump of about twenty long rather drooping white bristly hairs ; 

 sides of the mouth shining black; chin-beard whitish, rather slight but 

 extending more conspicuously on to the lower part of the back of the head ; 

 back of the head almost flat but the lower half slightly pufied out in profile 

 and with a rather broad and conspicuous glistening white postocular space 

 which extends to rather above the middle and then ceases without narrow- 

 ing to a point, and bearing on the upper half eight to ten pale yellow 

 postocular hairs which are neither strong nor bristly ; the back of the head 

 IS shining black behind and above the shimmering white margin and bears 

 numerous fairly long brownish yellow hairs amongst which a pair of post- 

 vertical hairs (hardly bristles) may be detected; frons brilliantly shining 

 black, quite bare, deeply sunk as usual, and with the ocellar space highly 

 elevated and bearing minute pale pubescence behind and above; antennal 

 prominence narrow but fairly high and sharply defined and with very slight 

 pubescence on its sides ; collar brilliantly shining black with sparse erect 

 pale hairs on its sides. Proboscis shining black, with the usual dorsal pubes- 

 cence near the tip brownish yellow but that beneath near the base very slight 

 and greyish white ; palpi black, very short, being only about a quarter the 

 length of the proboscis, and bearing towards the tip porrect greyish white 

 bristly hairs. Antennas rather long ; the two basal joints black but appear- 

 ing dull and brownish from minute brown tomentum, and bearing very slight 

 brownish yellow or almost black bristly pubescence which is rather longer 

 and more obvious on the underside ; basal joint long and thin, about twice 

 as long as the second joint ; second joint but little cup-shaped ; third joint 

 hardly so long as the two basal ones together, dull brownish black, and 

 bearing a few small dorsal bristles before the middle ; style thick but com- 

 paratively short, about a quarter the length of the third joint. 



Thorax brilliantly shining black and impunctate except where densely 

 covered with brownish yellow tomentum and pubescence ; the middle stripe 

 brilliantly shining but divided by a narrow line of tomentum and dying out 

 at about two-thirds down the disc ; side stripes broad but less regular, 

 beginning broad in front close to the middle stripe but quickly diverging 

 and extending almost to the hindmargin though interrupted by a cross-band 

 of tomentum at about half-way between their front and the suture, becoming 

 rather contracted after the suture, and then bending outwards a little over 

 the dark chestnut postalar calli ; the brownish yellow tomentum is conspicu- 

 ous on all the rest of the disc, and wherever that is present there is a rather 

 sparse short similarly colored pubescence. Bristles ; one prsesutural distinct ; 

 one distinct supra-alar followed by two or three weaker ones, and the 

 pubescence from them to the postalar calli rather strong. Pleurae brilliantly 

 shining black and impunctate except on the " shimmer stripes " ; front stripe 

 beginning rather narrow at the hind upper corner of the mesopleurse but 

 soon widening and extending down the front margin and becoming wide and 



