932 DR. A. G. BUTLER ON BUTTERFLIES [Dec. 4, 



69. Nychitona medusa, var. alcesta. 



Papilio alcesta, Cramer, Pap. Exot. iv. p. 175, pi. ccclxxix. A 

 (1781). 



Nairobi forest, March 20 : Euarka Eiver, 5500 feet, April 27, 

 1900. 



" An old friend, I think from Tana Eiver ; the first of its 

 species I have seen in these parts."' (R. C.) 



" This frailest of frail butterflies frequents dark forest, and 

 rarely is seen in the sunshine. Its flight is ridiculously weak. 

 Like a Kestrel it hovers over the same spot, only a few inches 

 from the ground, for minutes on end, without either materially 

 advancing or receding." (R. C.) 



Prof. Aurivillius is of opinion that A r . medusa and A 7 , alcesta are 

 distinct species. He may be right ; but I must confess that I am 

 sceptical as to the value of the characters upon which he separates 

 them. Every gradation of size exists from the largest N. medusa 

 to the smallest A', alcesta : the apical black patch sometimes borders 

 the outer margin to below vein 2, sometimes (in the large form) 

 only extends to just below vein 6 ; the discal spot in the large 

 form is sometimes crossed by veins 3 and 4, and in the small form 

 sometimes scarcely extends above vein 4. If it be correct that, 

 whereas A. medusa $ sometimes takes the form of A T . immaculata, 

 A 7 , alcesta $ always takes the form of N. nu/Aa, that might possibly 

 serve to distinguish the females ; but, for the present at any rate, 



I do not see my way to regarding the genus as consisting of more 

 than one very widely distributed and variable species. 



70. Colias electo, var. edusa. 



Papilio electo, Linnaeus. Cent. Ins. p. 21 (1763). 



? $ (C. Mice type), Fort Smith, May 28 ; Lali flats, 7850 feet, 

 Kikuyu forest, Dec. 19, 1899. 



5 (C. edusa type), Nairobi plains, 5400 feet, April 12, 1900. 



" On Lali flats, which are open grass-land surrounded by black 

 forest, C. edusa is far and away the most plentiful butterfly and 

 could be taken in almost any number. Quite ten if not fifteen 

 per cent, of the females seen are this pale-coloured variety." (R. C.) 



71. Tebias brigitta, var. zoe. 



Terias zoe, Hopffer, Monatsb. k. Akad. Wiss. Berl. 1855, 

 p. 640 ; Peters' Eeise n. Mossamb., Ins. p. 369, pi. xxiii. figs. 10, 



II (1862). 



2 $ , Eoromo, Dec. 14, 19, 29, 1899, Jan. 14, 1900 ; Mayi inoru 

 flat, Eeb. 10 ; <Jd, Ikwiaku, 7600 feet, Feb. 27; Nairobi plains, 

 5400 feet, April 5, 12, 14, 1900. 



72. Terias boisduvaliana. 



Terias boisduvaliana, Mabille, Hist. Mad., Lep. i. p. 253, pi. 32. 

 figs. 4, 5 (1885-7). 



