1916] 



Forbes — On the Tympamim of Certain Lepidopfera 



187 



sally and ventrally is as before, but in the pleural region above the 

 spiracle there has developed a bulla exactly like that of the Geomet- 

 ridse externally, but instantly distinguished from it by the fact 

 the spiracle lies on its lower edge. A cursory examination suggests 

 that it has developed out of the remaining rudiments of pleurites. 

 The thorax shows more or less trace of the curious modification 

 described for the Noctuida\ but the venter of the abdomen is 

 typical. 



Fig. 3. Same view of Caiocala porta, showing third, or 

 usual Noctuid type of tympanum. The cover, or alula of the 

 hind wing is drawn forward, and the posterior edge is turned 

 back to expose the spiracle and structures within the tym- 

 panum. 



