144 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Diplrra. 



PoLYTOCUS, gen. nov. 



Head. — In side view the irons slopes downwards to the front margin and the 

 face upwards from tlie retreating mouth, so that the forehead is well produced. The 

 antennae are inserted exactly on the end (see fig. 9). Frons flat and broad, un- 

 furrowed, with the eye-margins, on which 

 are the obital bristles, broad. Face broadly 

 keeled in the median line, with narrow 

 cheeks. Head somewhat swollen behind. 

 The front of the vertex, the jowls, and back 

 of head with bristly hairs. Eyes bare ; 

 small for the size of insect ; longish-oval, 

 with the long axis roughly vertical ; less 

 than half the depth of the head. Antennae 

 porrect ; 1st joint of moderate size, 2nd 

 and 3rd of nearly equal length, each about 

 three times the 1st ; 2nd hairy, with a 

 long anterior bristle. Arista fine, bare, 

 basal joints slightly swollen. Palpi stout 

 and bristly, especially at the ends. Pro- 

 boscis with a broad backward-projecting 

 end. 



Chaetotaxtj. — Bristles very well developed, 

 vertical the same ; outer verticals diverging ; 

 pairs of orbital, the front pair much diverging ; 



1-1-3 dorso-central bristles ; weak but fairly long praescutellars ; 

 humeral ; prothoracic ; praesutural ; 2 noto-pleural ; 3 supra-alar 

 pleural. 



Wings long, rather narrow and pointed. Main branch of 1st vein 

 stout, its junction with the costa being well along the latter, somewhat less than 

 half the wing-length from the insertion ; auxiliary branch of 1st ( = mediastinal) 

 evident throughout, very close to main branch at base, but with the end merging 

 in the costa far before the main branch, thus leaving a long pale " stigma " recalling 

 that of Heteromyza. Veins 2, 3, and 4 parallel at ends ; cross-vein somewhat beyond 

 the middle of the discal cell ; costa extending to junction of 4th vein ; .5th vein 

 not quite reaching wing-margin : hind cross-vein straight and somewhat olilique. 

 Basal and anal cells small. 



The costa is provided with a remarkable series of spines. In addition to the 

 ordinary short bristling on the costa, there is a row of stout bristles, whicli alter- 

 nately bend slightly below and above the plane of the wing. These bristles extend 

 from just before tlie humeral or basal cross- vein to just before the junction of the 

 2nd vein. (These spines are rather easily knocked off.) 



Legs. — Preapical bristles and spurs on all the tibiae ; the middle til)ia witli a 

 multiple spur or crown of bristles. Claws and pads well developed. 



Abdomen cylindrical, with fairly small male genitalia, and in the female with 

 the last segments forming a shoi-t ovipositor. 



Post-vei'ticals nearly parallel : inner 

 long ocellars pointing forwanls ; two 

 no vibrissae. 



4 scutelhir ; 

 ; 2 sterno- 



= subcostal) 



