ISCHNOGASTEE. 377 



legs slender, nearly smooth ; the intermediate tibiae with a short 

 anterior and very long posterior slender apical spine ; tarsal claws 

 unidentate in the middle below. Wings long, ample ; radial cell of 

 the fore wing long, narrow, acute at the apex, which reaches very 

 nearly to the apex of the wing ; four cubital cells, the 1st and 2nd 

 subequal on the cubital nervure, the 2nd nearly forming a right- 

 angled parallelogram, the 3rd square or nearly square, shorter 

 than the 2nd, the 4th small, irregular, continued to the apex of 

 the wing ; the 2nd cubital cell receives both recurrent nervures 

 close to its base and its apex respectively. Abdomen remarkable 

 for its long thin petiole, which is nearly cylindrical with the apex 

 suddenly clavate ; in some species the base of the 2nd segment 

 is also distinctly petiolate, in all it is attenuate, smaller than the 

 apex of the first segment ; 3rd and following abdominal segments 

 forming a more or less acute cone. 



The species of this genus seem to me to form the links between 

 the Solitary and Social Wasps, as they not only combine the struc- 

 tural characters of the two families of the Biplo^dera, but different 

 sections of the genus have different nesting- habits — the larger 

 species making, as a rule, solitary nests constructed by one pair, 

 d and $ ; the smaller species living in a many-celled social nest 

 in tiers constructed by the community. In the ' Journal of the 

 Bombay Natural History Society ' for 1890, vol. v, I figured the 

 two nests. 



Key to the Species. 



A. Colours black, with yellow or red markings, 



a. Head and thorax black, with yellow 



markings. 

 a'. Clypeus yellow, with an irregular 



square medial space black, not reach- 

 ing its apex ; median segment with 



a reversed T -shaped yellow mark on 



each side I. micans, p. 378. 



b'. Clypeus yellow, without a black medial 



space ; median segment with a yellow 



spot on each side at apex I. fraterna, p. 378. 



c'. Clypeus black, with a small central 



yellow spot ; median segment black 



immaculate I. scitula, p. 379. 



b. Head and thorax black with red mark- 



ings I. rtifomaculata, p. 379. 



B. Colours rufescent brown or ferruginous 



with yellow markings. 



a. Median segment very finely transversely 



striate /. iiiyrifrons, p. 379. 



b. Median segment smooth. 



a'. Median segment with a vertically- 

 impressed medial line ; of compara- 

 tively small size. Length 12 mm.. . I. nitidipentiis, j>. 380. 



b'. Median segment without a vertically- 

 impressed medial line ; of compara- 

 tively large size. Length 17-l&i mm. /. eximia, p. 380. 



