366 



MR. ROBERT SHELFORD ON 



of tlie genera. Ana'plecta and Plectoptera there is every grade of 

 transition. In a typical species of Anaplecta the apical triangle 

 has become a large parabolic area, now known as the apical area, 

 almost equal in size to the rest of the wing, over which it is 

 doubled back when the wing is folded (text-fig. 44). In the 

 species Anaplecta variipennis Shelf., the passage from an apical 

 triangle to an apical area can be traced ; for some individuals 

 exhibit the Chorisoneura type of wing-structure ; in othei\s is 

 seen the extension of the apical triangle by the widening out of 

 the angle made by the intercalation of this area between the 

 anterior and posterior parts of the wing; fi.nal]y, some specimens 

 exhibit the complete development of the apical area, with its 

 straight base-line, cutting the wing transversely into two halves, 

 so that the longitudinal veins of the anterior part of the wing 

 and the first axillary veins of the posterior part, no longer impinge 

 on the outer margin of the wing, but on the base-line of the 

 apical area. The summit of wing-development is attained by 

 Dlploptera dytiscoides Serv., for in this species the apical area is 

 closely veined, though the veins are not in organic continuity 

 with those of the other part of the wing. 



Text-fig. 45. 



Frosoplecta nic/rovarieffata. 

 Wing expanded {a) and folded (b). The pseudapical area is shaded. 



A cursory glance at the closed wing of any species of Proso- 

 plecta (text-tig. 45) leads the observer to suppose that it is 

 constructed on the same principle as tliat of Ectohms and Thegan- 



