584 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



in the other orders of insects. In the Tenthredinoidea it is present 

 only in Macroxyelaferrngmea^ and even here is only faintly indicated. 

 In the LydidiB, there is a broad thickening- at the base of subcosta and 

 a similar thickening- in the Meg-alodontidte (tig. 92) between costa and 

 Sc + R + M that may be homolog-ous with this cross-vein. 



THE SUBCOSTAL AREA. 



Subcosta does not occur in the Hymenoptera outside the superfamil}^ 

 Tenthredinoidea, and here only in the families Xyelida^ (tigs. 31-35) 

 and Lydid;« (figs. 36-43). In most of the genera of these families 

 subcosta extends midway between costa and R+M. Near its apex it 

 divides into Sc^, which ends in the margin of tiie wing, and Sc^, which 

 anastomoses with R+M and ends in the margin of the wing at the base 

 of the stigma. Behind the stem of subcosta there is found the cell Sc 

 and behind and bej^ond the vein Sc^ the cell Sc^. In Megaxyela (tig. 

 31) and Odontophyes (tig. 32) the cell Sc^ is very small, due to the 

 great length of subcosta. Subcosta divides into Sc^ and Sc2 midwa}^ 

 between the origin of media and the radial sector. In Macroxyela (tig. 

 33) this separation takes place just beyond the origin of media, while 

 in the Lydidje this separation is a considerable distance before the 

 origin of media. These wings show that there is a progressive migra- 

 tion of the origin of Sc^ and Sc.^ from near the origin of the radial 

 sector to a position near the base of the wing. In Xyela (fig. 35) and 

 Manoxyela (tig. 34) the stem of su])costa is closely appressed to R+M, 

 though it is never coalesced with it, so far as I have been able to 

 observe, almost obliterating the cell Sc and causing the branch Scj to 

 extend like an oblique cross-vein from R+M to the wing margin. In 

 NeuTotoma^^^. 36) the free part of Sc^ has completely atrophied, while 

 the remainder of the vein is normal. An interesting related condition 

 is found in certain of the large species of Siricida?, as Trernex colmnha 

 (fig. 91), where the area of the wing situated between costa and R+M 

 is almost as strongly chitinized as the veins themselves. In wings 

 mounted in balsam it is possible to trace as a pale line a condition of 

 subcosta similar to that found in NeuTotoma. This seems to indicate 

 that subcosta has been suppressed in two ways, first, by the close 

 appression of its stem to R+M and its probable later coalescence with 

 it, and, second, by the chitinization of the area between costa and 

 R+M, and in this manner doing away with the necessity for a vein to 

 stiffen this area. 



In all other Tenthredinoidea, where any portion of subcosta is pres- 

 ent, other than the apex of Scg, it is the free part of Scj. It extends 

 as a cross-vein between costa and R+M, and is usually spoken of by 

 the investigators on this superfamily as the intercostal cross-vein. It 

 is generally situated just in front of the radial end of the niedio- 

 cubital cross-vein, except in Xlpluydrla (fig. 85), where it is sometimes 



