NORTH AMERICAN EUCOSMHsTAE. 7 



(in extreme cases 3 and 4 fusing well before the termen), and for 

 vein 2 to become sharply bent upward before reaching termen. 



3. In hind wing venation : from a form with 6-7 approximate to- 

 ward base (" tortriciform"), with 3-4 short stalked, and with 5 bent 

 at base and closely approximate to the stalk of 3 and 4 ; to forms with 

 6-7 distinctly stalked, with 3 and 4 united, and with 5 tending to be- 

 come straight and moving away from 3 and 4 at the base. 



4. In secondary characters : from a smooth winged form with sim- 

 ple antennae and possessing the male costal fold but without the 

 other secondary sexual modifications; to forms with raised scales 

 on forewings, notched antennae or male sex scalings on the hind 

 wings. 



5. In genitalic development showing modification in several direc- 

 tions, all tending, however, to the following results : a loss of uncus, 

 socii, clasper, and costal hook of harpe (element of a divided, re- 

 duced, and modified transtilla) and a general simplifying of the 

 tegumen and harpes. The uncus disappears in three distinct ways : 



(a) by gradual weakening and reduction without narrowing 

 {EuGOsma-Epiblema group) ; (b) by narrowing, splitting to a bi- 

 fid hook and gradually becoming shorter and shorter till it disap- 

 pears but without becoming more weakly chitinized {Epinotia- 

 Ancylis group) ; (c) by bifurcation and reduction becoming in ad- 

 vanced types {Rhopohota^ Norma^ Kundrya) two short widely sep- 

 arated, wealdy chitinized projections from the posterior end of the 

 tegumen. 



The socii disappear (or lose their identity) in two ways, either by 

 gradual reduction {Rkyacionia) or by fusion with gnathos {Gyp- 

 sonoma, Gretchena^ Epinotia) . In the latter case, however, it does not 

 appear to be the socii which are disappearing. In fact, they become 

 broader, more triangular {Gypsonoma) or more stronglj^ chitinized 

 {Epinotia) . The gnathos becomes correspondingly smaller and more 

 restricted but in the close association and final fusion of the two 

 parts the identity of the socii is obscured. The most extreme devel- 

 opment is reached in Rhopobota where there is an almost complete 

 fusion of the two parts into a hairy, knobbed, porrected organ, only 

 the apices of which can be differentiated as socii and only a narrow 

 connecting band between the two porrected arms identified as the 

 free element of a gnathos. All the rest is a fusion of the two parts. 

 The gnathos itself is entirely lost only in Hystricophora. The harpes 

 imdergo various developments, in some forms acquiring spines on 

 the outer surface {Rhopobota^ Crocidosema) , but on the whole tend- 

 ing to lose the heavy spining from sacculus and the region bordering 

 the neck. These organs have a wide specific range of shape but the 

 general tendency is to a simple form with rather broad battledore 



