602 PROCEEDTNGS OF THE NATIONAL MUSEUM. vol. xxix. 



cera^ and Dieiocerii.s (fig. 79), the cross-vein is imich shorter, one-third 

 to one-fourth the length of this part of M^, 



The medio-cubital cross-vein in the generalized Tenthredinoidea is 

 transverse and subequal in length to the transverse part of M, but 

 there is considerable variation thi'oughout the various genera of the 

 other groups. Its departures from the generalized condition may be 

 divided into five groups. In the first of these the longitudinal part 

 of M has migrated along the transverse part of M, greatly increasing 

 the length of the cross-vein, although the cross-vein and the trans- 

 verse part of M retain relativel}^ the same position. This is shown in 

 the genera Trlchiosomn (fig. 59), Ldhidurge (fig. 78), DoleruH (fig. 49), 

 and Monoctenus (fig. 67). In the second group the length of the 

 cross-vein has been greatly increased by the migration of the trans- 

 verse part of M from its position at or near the base of the cell 

 M^+lst Mj to near its middle as in the genera Tenthredo (fig. 56), 

 Periclista (fig. 69), and Strongylog aster (fig. 51). In the Cephidse 

 this migration has proceeded so far that the transverse part of M is 

 joined to the cell M^+lst M^ near its apex. The third group is 

 represented by the genera Xiphydria (fig. 85), Macrophya (fig. 57), 

 Phymatoeera (fig. 71), Rhadinocerxa (tig. 70), and Lycaota (fig. 55). 

 In these genera there has been a combined migration of the longi- 

 tudinal part of M along its transverse part, together with a migration 

 of the transverse part of M toward the apex of the wing. The fourth 

 group is represented by the genus Pterygophorus (fig. 81), where the 

 longitudinal part of M has migrated toward M^ along the medio- 

 cubital cross-vein, resulting in a distinct shortening of the cross- 

 vein, in the fifth group there has been a migration of the transverse 

 part of M toward the apex of the wing, while the free part of M^ has 

 swung around from a longitudinal or oblique position to a transverse 

 one. Coordinated with the change in position of the free part of M^ 

 there has been a swinging forward of the part of cubitus on the Ibasal 

 side of the medio-cubital cross-vein until it has come into line with 

 the base of the longitudinal part of M, so that in this group the medio- 

 cubital cross-vein extends longitudinally instead of transversely. 

 This is practically the same condition as is found in the higher H^^me- 

 noptera and is shown by the genera Perga (fig. 81), Perreyla (fig. 80), 

 Acordulecera (fig. S3), and Loboceras (fig. 82). 



THE CUBITAL AREA. 



In the hind wings cubitus is represented by the long, straight vein 

 extending from the base of the wing to the medio-cubital cross-vein. 

 All trace of the free part of Cuj is wanting, and the same is true of 

 Cug .unless we homologize the short vein found in the Xyelid» (figs. 

 31-35) at the base of the wing with this vein. That this spur repre- 

 sents the free part of Cu.^ there can not be much doubt. That it is not 



