Chap. XI. BUTTERFLIES AND MOTHS. 397 



to entomologists the most useful character for detecting 

 the affinities of the various species. 



Now if we turn to the enormous group of moths, 

 which do not habitually expose to full view the under 

 surface of their wings, this side is very rarely, as I hear 

 from Mr. Stainton, coloured more brightly than the 

 upper side, or even with equal brightness. Some ex- 

 ceptions to the rule, either real or apparent, must be 

 noticed, as that of Hypopyra, specified by Mr. Wormald. 12 

 Mr. E. Trimen informs me that in Guenee's great work, 

 three moths are figured, in which the under surface is 

 much the most brilliant. For instance, in the Australian 

 Gastrophora the upper surface of the fore-wing is pale 

 greyish-ochreous, while the lower surface is magnificently 

 ornamented by an ocellus of cobalt-blue, placed in the 

 midst of a black mark, surrounded by orange-yellow, 

 and this by bluish-white. But the habits of these 

 three moths are unknown ; so that no explanation 

 can be given of their unusual style of colouring. Mr. 

 Trimen also informs me that the lower surface of the 

 wings in certain other Geometrse 13 and quadrifid Noctuae 

 are either more variegated or more brightly-coloured 

 than the upper surface ; but some of these species have 

 the habit of " holding their wings quite erect over their 

 " backs, retaining them in this position for a considerable 

 " time," and thus exposing to view the under surface. 

 Other species when settled on the ground or herbage 

 have the habit of now and then suddenly and slightly 

 lifting up their wings. Hence the lower surface of the 

 wings being more brightly-coloured- than the upper sur- 



12 ' Proc. Eut. Soc' March 2nd, 1868. 



13 See also an account of the S. American genus Erateina (one of 

 the Geometrse) in ' Transact. Ent. Soc.' new series, vol. v. pi. xv. and 

 xvi. 



