596 



AN INTRODUCTION TO ENTOMOLOGY 



fauna ; one of these, Sthenopis purpurdscens, is represented in Fi^re 

 721. 



The larva of Sthenopis argenteomaculatus bores in the stems of the 

 speckled or hoary alder {Alnus incana) ; that of Sthenopis thule, in 

 willow. 



Suborder FRENAT^ 



The members of the Frenatse are most easily recognized by the 

 fact that the venation of the hind wings differs markedly from that 

 of the fore wings, being much more reduced. In this suborder, 

 vein Ri of the hind wings coalesces with subcosta, the two appearing 

 as a single vein, except that, in some cases, a short section of the base 

 of Ri is distinct, presenting the appearance of a cross-vein between 



Jc/^ 2d A 



I si A 



Fig. 722. — Wings of Prionoxystus robinicE. 



radius and subcosta (Fig. 722, Ri). After the separation of vein Ri, 

 the radial sector continues unbranched to the margin of the wing 

 (Fig. 722, Rs). Rarely, as in some members of the Gracilariidce and 

 of the Cosmopterygidas, vein Ri of the hind wings is free, not co- 

 alesced with vein Sc. 



The essential characteristic of the Frenatae is that they are 

 descendants of those primitive Lepidoptera in which the two wings 

 of each side were united by a frenulum. This fact should be clearly 

 understood, for in many of the Frenatae the frenulum has been lost. 

 The loss of the frenulum in these cases is due to its having been 

 supplanted by a substitute for it, by an enlarged humeral area of the 

 hind wings, which causes the two wings of each side to overlap to a 



