tJie Geometrina of the European fauna. 59 



Structural variation within specific limits is in this 

 family slight ; the principal diversity is in the origin of 

 vein 6 of the fore wings, which frequently rises either 

 out of 9, or separate, in different individuals of the same 

 species ; this occurs more or less in nearly all the 

 genera, and is therefore not specially mentioned in the 

 diagnoses. 



The family is a dominant one, and contains a very 

 great number of species, spread all over the world. The 

 uniformity of structure throughout these is remarkable, 

 and their systematic classification is proportionately 

 difficult. Probably Lytlina is the oldest European form 

 of the family, though the New Zealand genus Notoreas 

 is still more ancestral, and in fact fulfils all the require- 

 ments of the primitive type. This must be derived from 

 a genus closely approaching, or even perhaps identical 

 with, the Australian Ocnone in the Monocteniadce, to 

 which in Europe Brephos is the nearest approximation. 

 From Notoreas springs immediately the Xanthorhoe 

 group, and also through Dasyuris the Hydriomena group. 

 From the latter the four groups typified respectively by 

 Tephrodystis, LobopJiora, Eacestia, and AstJtena, are 

 given off" as so many diverging branches, which are 

 themselves again variously branched. A linear arrange- 

 ment of the genera of course cannot display this rela- 

 tionship effectually, but the main features are set forth 

 above, and the natural affinities of the other genera con- 

 stituting the various groups are explained under their 

 respective heads. 



Tabulation of Genera. 



1. Posterior wall of areole absent '215. Cataclysiie. 



Posterior wall of areole present . . . . . . 2. 



2. Posterior tibitS without median spurs . . . . 3. 

 Posterior tibiae with all spurs present . . . . 4. 



3. Hind wings in ^ with inner marginal lobe . . 2. Trichopteryx. 

 Hind wings in (^ without lobe 11. Gymnciscelis. 



4. Areole simple . . . . . . . . • . 5. 



Areole double .. .. .. .. .• 17. 



5. Fore wings with vein 11 running into 12 . . <>. 

 Fore wings with vein 11 free from 12 . . . . 7. 



0. Fore wings in ^ with rough projecting hairs on 



costa 9. Phrissogonus. 



Fore ^\'ings in J without rough hairs on costa 10. Chlokoclystis. 



