BUTTERFLIES. 155 



305. Castalius elna, Hewitson. 



Common up to 4,000 or 5,000 feet from April to October, It is 

 seasonally dimorphic, but the difEerent forms have not been named. 

 Mr. Elwes records C. roxics, Godart, from Sikhim, but it does not, 

 I believe, occur further north than Burmah. ' 



306. Castalius decidia, Hewitson. 



Common at low elevations from April to October. It is seasonally 

 dimorphic, the rains'-form being 0. hamaius, Moore, an intermediate 

 form is the true C. decidia, the dry-season form is C, interruptiis, de 

 Nicdville. 



307. Polyommatus bceticus, Linnaeus. 



Found in Sikhim from the level of the Terai up to 10,000 feet, 

 but never very commonly at the higher elevations. 



308. Amblypodia anita, Hewitson. 



Mr. Elwes records a single specimen from Sikhim. It not at all 

 improbably occurs in the Terai, but is not likely to be found in the hills. 



309. Iraota timoleon, Stoll. 



Mr. Otto MoUer obtained three males and six females of this 

 species at low elevations and in the Terai, some taken in July, but 

 it is a very rare species in Sikhim. 



310. Ikaota Maecenas, Fabricius. 



Mr. Otto Moller had only three female specimens in his collec- 

 tion, all from the Terai, taken in April, November, and December, 

 so it must be even rarer than /. timoleon, Stoll, from which as a 

 species it is very doubtfully distinct, in which opinion Mr. Dudgeon 

 concurs. He has received numerous specimens of both species taken 

 together in Daling, all in May, and has seen the males flying round 

 India-rubber and other trees of the genus Fims at 1,500 feet. 



311. SuRENDRA quercetorum, Moore. 



Almost throughout the year, at low elevations. Both sexos com- 

 mon, but the female commoner than the male. The larva feeds on 

 difEerent species of Acacia. 



312. Arrhopala centaurus, Fabricius, 



The local race of this species found in Sikhim, Bhutan, and 

 Assam has been named A. pirithous by Mr. Moore. It is a very 

 common species at low elevations in Sikhim, and occurs nearly all the 

 year round. The larva feeds on the young leaves of the sal tree, 

 and is carefully attended by the large and fierce red tree ant, 

 CEcophylla smaragdina, Fabricius. 



313. Arrhopala silhetensis, Hewitson. 



Excessively rare. I possess a single male example from Jalpai- 

 guri, obtained by Mr. A. V. Knyvett and kindly given to me. The 



