PLETCHBE— LBPIDOPTBEA. 317 



V. On the Distribution or the Lepidoptera in the Islands op 



THE Indian Ocean. 



Chagos. 

 Prom an entoraogeograpliical point of view the Chagos Archipelago is by far the most 

 interesting of the groups of islands which we visited. Situated in the middle of the 

 Northern Indian Ocean, separated from the nearest land * by 24)0 miles of open sea, and 

 encircled by ocean-depths of over 2000 fathoms, these islands yield a problem of 

 peculiar fascination in the study of the forms of insects found in them, as possibly 

 affordiug some indication of the manner in which they have arrived at so remote a spot. 

 With this object in view I have attempted the following analysis of the non-endemic 

 Lepidoptera. 



(1) Species common to the African, Indian, and Australian regions : — Prodenia 

 tutor alls, Remigia frugalis, Ptusia chatcytes, CosmopJdta erosa, Sradina admixtatis, 

 Zinckenia fascialis, Marasmia venitiatis, Glyphodes indica, Trichoptitus defectatis. Of 

 these, all occur in Ceylon and probably all in Sumatra-Java also. As the Chagos fauna 

 contains no elements of an exclusively African character, we can omit Africa as the 

 original home of the above-named species. Granting a possible derivation from Ceylon 

 via the Maldives for numbers 5, 6, and 8, and omitting T. defectatis, whose distribution 

 is insufhciently known, we are left with the fact that the remaining five species (nos. 1-4, 

 7) are all found either in Christmas Island or in the Cocos-Keeling group, a fact which 

 seems to point to their original entrance into the Chagos by way of these other islands 

 from the Malayan or Australian regions. 



(2) Species common to the African and Indian regions : — Eriopus maittardi, Cultadia 

 admigratetta, Syngamia jloridalis, Nacoteia nipJieatis. Of these, the first three are found 

 in Ceylon and in Sumatra-Java, and may have gained an entrance into the Chagos from 

 either direction. I think it unlikely that any of them are derived direct from Africa ; 

 certainly Syngamia Jloridalis, which is a particularly conspicuous species, has not been 

 recorded from any of the East African Islands. N. nipheatis may be assvimed to have 

 come from Ceylon through the Maldives, and in connection with this assumption it is 

 interesting to note that the present distribution of nipheatis in the Chagos Archipelago 

 (Peros Banhos and Salomon Atolls only) may possibly point to its recent introduction 

 from a northerly rather than from a south-easterly direction. 



(3) Species peculiar to the Indian region : — Ophiusa honesta, Acherontia lacliesis, 

 Hypolimnas boliua, Endotricha mesenteriatis, Mabra eryxalis. All of these occur in 

 Ceylon. E. mesenterialis has doubtless come through the Maldives. The other four 

 (of which three are very large and conspicuous forms, not likely to have been overlooked 

 in the Maldives) may have come from either direction. 



(4) Species common to the Indian and Australian regions : — JJfetkeisa putcheltoidesf, 



* Addu Atoll, the southerumost of the llaldive Group. 



t U. pulchelloides seems to beloug properly to the Indo-Australian region, although it is found as far west as 

 Cargados Carajos, the Amirantes, and Seychelles (but not in Africa or Madagascar, so far as is known at present). 

 SECOND SERIES. — ZOOLOGY, VOL. XIII. 42 



