1871.] MR. A. G. BUTLER ON ANGOLAN BUTTERFLIES. 721 



which may furnish one with a clue to the reason for the existence of 

 this osseous covering, whether such is for protection or whether a 

 part of the auditory apparatus. 



Of the twenty-four Indian genera adverted to, we find some resi- 

 dents in waters of the plains, also in rivers on the hills with or 

 without alpine sources. 



Amongst the seventeen resident in waters of the plains and not ex- 

 tending their range into hilly regions we find in seven the air-vessel 

 is free, viz. in Rita, Hara, Pseudeutropius, Macrones, Callichrous, 

 Wallago, and Panyasius ; whilst in ten it is more or less enclosed 

 in bone, viz. Ailia, Ailiichthys, Sisor, Bagarius, Saecobranchus, 

 Silundia, Eutropiichthys, Gagata, Clarias, and Hemipimelodus. 



Amongst those residing in rivers of the plains and extending their 

 range into those of the hills which have or are destitute of alpine 

 sources, we perceive as follows : — 



Of those four genera which are found in the waters of the plains 

 as well as in hill-rivers with alpine sources, all have their air-vessels 

 enclosed in hone, viz. Amblyceps, Pseudecheneis, Exostoma, and 

 Glyptosternum ; whilst the last three genera have representatives in 

 the next division, and all are furnished with an adhesive apparatus. 



Of the three genera found in rivers of the plains and also in those 

 of hills destitute of alpine sources, none have their air-vessels enclosed 

 in bone, viz. Silurus, Olyra, Akysis. 



From the foregoing it appears that the majority of the genera of 

 Indian freshwater Siluroids have their air-vessels enclosed in bone ; 



That no true Indian, wholly marine Siluroid has its air-vessel 

 enclosed in bone ; 



That amongst the Siluroids of the hilly regions, those which ascend 

 rivers having alpine sources have the air-vessel enclosed in bone ; 



That those which ascend rivers not snow-fed do not appear of ne- 

 cessity to have their air-vessels thus protected. 



Space and time will not permit me to enter further on this subject 

 at present, which, however, I hope to do at no very distant date. 



2. On a small Collection of Butterflies from Angola. 

 By A. Gr. Butler, F.L.S., F.Z.S., &c. 



[Keceived November 8, 1871.] 



The present collection, though it only contains twenty-four species, 

 of which three are new to science, is interesting as an addition to our 

 knowledge of the Butterflies of Angola ; it was made at Loanda, 

 the capital of the Portuguese settlements in Angola, situated at 

 1 000 feet elevation, at between 8° and 9° S. lat. Fourteen of the 

 species in the following list were also in my list of the Diurnal Lepido- 

 ptera taken by Mr. Ansell at Kinsembo. This collection has been 

 lent to me for determination by my friend and brother lepidopterist 

 R. Meldola, Esq. 



