610 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



When the conditions existing in such a wing as Blennocanvpa alter- 

 nipes are compared with those found in the front wing of Macroxyela 

 ferruginaa the difference is ver}' apparent. The trusses in the wing 

 of Macroxyela have not been numbered. Only the most important 

 have been indicated. From their fewness in number the reader might 

 be led to conclude that the wing of Macroxyela had not been done full 

 justice, but when the form of the cell areas is taken into consideration, 

 all of them being either trapeziums or trapezoids in form, it is seen 

 that this arrangement is one of tlie weakest possible. In such an 

 arrangement as this each angle of each cell is the apex of a truss, 

 which can have no other function than to stiffen the sail area. Con- 

 sequentl^y, if all the trusses found in the wing of Macroxyela had been 

 indicated on tlic drawing, it would have residted in tliis wing being 

 apparently much more efficient, at least in numl)er of trusses, than 

 that of Blennocariijxi. Although there are several trusses in the wing 

 of Macroxyela^ yet it is a striking fact that these trusses are not nearh^ 





^. v-.^ ^^-~-"}-^, 



>^ 



\ I 



Fk;. I.S.— The front wing of macroxyela an'i> its trusses. 



SO efficiently placed (tig. 18). There is not so great a concentration 

 of the stress to one region. The trusses instead of stiffening a defi- 

 nite area are scattered over the entire wing surface. Veins that in 

 Blennocampa are constituents of important trusses are of little more 

 value than to keep the wing membrane expanded in Macroxyela. 

 vSome of the most prominent differences are the position of the niedio- 

 cubital cross-vein and the origin of Mj, the course of the veins bound- 

 ing the cell Mg, the position of the radial cross-vein, the narrowing of 

 the cells included between the veins R., and Mj, and the course of the 

 transverse part of Mj. 



The adults of Macroxyela ferruginea are connnon at Ithaca. The 

 larva* feed on the leaves of the numerous elms found along the walks 

 on the campus. The adults are very inactive, so nnich so, in fact, 

 that they will lie still and allow themselves to be crushed underfoot 

 on the walks. When they are distur])ed in such a way as to be com- 

 pelled to use their wings, they have a slow hunbering flight and soon 

 alight again; — that is, the generalized condition of their wings as 



