lix 



their occurrence and flight together on several days. It is 

 probable, however, that Nychitona, with which both natur- 

 alists were very familiar, was proportionately commoner than 

 the captures indicate. 



The 26 examples of Nychitona were somewhat sharply 

 separable into a larger form with an expanse of 1| to If in., 

 and a smaller form of about IJ in. Both lacked the spot 

 in the fore-wing. The larger appeared to be a small variety 

 of N. medusa f. immacuJata Auriv., and, from the form of 

 the apical black margin to the fore-wing, five males of the 

 smaller form (taken July 23, 27 and 28) also appeared to be 

 immaculata. Judging from the same feature, the two 

 remaining males resembled N. alcesta Cr., f. nwptilla Auriv., 

 but were smaller, while the two females, entirely without 

 the black apical margin, appeared to belong to them. These 

 females resembled nwpla Butl., as figured by Aurivillius 

 (Seitz's " Macrolepidoptera," xiii, pi. 106), but were smaller. 

 The two males, coming from the locality of nwptilla (Ruwen- 

 zori), are almost certainly this form, and the two females 

 may be the same, or the form described by Butler, although 

 here the locality was Angola. Aurivillius, on p. 31 of the 

 above-mentioned work, speaks of nwpta, as entirely white, 

 but Butler (Cist. Ent., Vol. i, p. 175) describes the apical 

 edge of the fore-wing as " slightly dusky," and, this being so, 

 it does not seem to be distinguishable from a pale-edged 

 nuptilla. The distinction between medusa and alcesta, or 

 between any other different species that may be supposed 

 to exist in the varied African forms of Nychitona, requires 

 for its establishment a structural or genetic foundation, and, 

 until this is supplied, the extent of variation and transition 

 suggests that they should all be regarded as forms of Cramer's 

 7nedusa. 



As regards the mimetic association, the larger forms in 

 the following table would resemble in size the majority of 

 Pseudopontia, while the black apical margin, invisible in 

 flight and merely causing the insect to appear somewhat 

 smaller, would not become a distinguishing feature. The 

 smaller forms of Pseitdopontia would similarly resemble the 

 smaller ones of Nychitona. 



