the Gcometrina of the European fauna. 51 



Hind wings with 8 not connected with cell by 

 bar near base . . . . . . . . • • 4. 



4. Hind wings with 8 very shortly anastomosing 



with cell near base, thence rapidly diverging 4. SxEBr.uiDiE. 

 Hind wings with 8 approximated to or anastom- 

 osing with cell to middle or beyond . . . . 5. 



5. Hind wings with 8 free or shortly anastomosing 



with cell near base only 2. Monocteniad.-e. 



Hind wings with 8 anastomosing with cell to 

 beyond middle, or connected with it by bar be- 

 yond middle 1- Hydkiomenid.e. 



It seems to me that at i^resent clearness and intelligi- 

 bility is best attained by treating all these six groups 

 as equivalent families ; they are in practice all easily 

 separated by structure, and are also without doubt 

 natural groups which are conveniently discussed as 

 wholes. But the distinctions between families 2 — 5 are 

 of a less marked character, less absolute, and tend more 

 to be destroyed by intermediate gradations ; and there 

 would be much to be said for treating these four as sub- 

 families of one family [Geometridce), to be accorded e(iual 

 rank with the other two, the Hijclriomenicke and Stlido- 

 semiche. I conceive it to be a question of convenience, 

 and a matter of judgment rather than of fact, and 

 probably the most careful students may be found to hold 

 various opinions on the point. 



1. HYDKIOMENID.E. 



Fore wings with vein 10 rising separate, anastomosing with 11 

 and 9, or rising out of 11 and anastomosing with 9. Hind wings 

 with vein 5 fully developed, 6 and 7 almost always stalked or from 

 a point, 8 anastomosing with upper margin of cell from near base 

 to beyond middle, or sometimes approximated only and comiected 

 by bar or shortly anastomosing beyond middle. 



The peculiar anastomosis of vein 8 in the hind wings 

 is highly characteristic of this family ; it does not exist 

 in the same form in any other family of the Lepidoptera, 

 save in the case of one or two exceptional genera. It is 

 occasionally so far modified as to be represented only by 

 a connecting bar beyond middle of cell ; this structure, 

 occurring especially in the males of the Lobophora 

 group, is clearly caused by a tendency to lateral expan- 

 sion of the wing, which takes place usually in com- 

 pensation for the absorption of a considerable portion of 



