370 Mr. A. Alcock on the Datkyhial Fishes 



These are its characters : — Mandibles sliort and broad, nar- 

 rowed to a thin edge and feebly toothed on the inner side, 

 sharply incurved and pointed at the tip, with their edges 

 superposed along nearly their whole length when closed. 

 Antennaj scarcely reaching to half the length of the elytra. 

 The four posterior tibijB differ from those of the males in 

 being simple and not dilated. The last ventral segment of 

 the abdomen is narrowly rounded and somewhat pointed at 

 the apex ; in the male this segment is transversely truncated. 

 The hind cox^e are rather widely separated and the intercoxal 

 process of the abdomen is obtusely rounded in front; in the 

 male the coxaj are closer together and the intercoxal process 

 is sharply pointed in front. 



In the Indian genus Acanthophorus, as represented by A. 

 serraticollis, Oliv., the same kind of variation is found. 



LIV. — Natural History Notes from II.M. Indian Marine 

 Survey Steamer ^Investigator,^ Commander Alfred Carpen- 

 ter^ B.N., D.S.O., commanding. — No. 13. On the Bathybial 

 Fishes of the Bay of Bengal and neighbouring waters^ 

 obtained during the seasons 1885-1889. By Alfred 

 Alcock, M.B., Surgeon-Naturalist to the Survey *. 



Contents. 



§ 1 . Outline of the Hydrography of the Region. 



§ 2. List of the Fishes, with Descriptions of the new Species. 



§ 1. Outline of the Hydrography of the Region. 



The bathybial fishes hitherto collected by the ' Investigator ' 

 are all from the arm of the Indian Ocean which intervenes 

 between the Indian and Malayan peninsulas — the sea which 

 is generally spoken of as the Bay of Bengal. Tliis vast 

 stretch of water, which occupies roughly the meridians be- 

 tween 78° and 98° E. and the parallels between 5° and 22° 

 N., consists of three distinct basins, namely the Bay of Ben- 

 gal proper in the centre, the Gulf of Manaar to the south- 

 west, and the Andaman Sea on the east. And it will be 

 fitting to prelude the account of the fish-inhabitants of their 



* Communicated by the Superintendent of the Indian Museum, Cal- 

 cutta. 



