376 Mr. A. Alcock on the Bathybial Fishes 
These are its characters :—Mandibles short 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. 
Antenne scarcely reaching to half the length of the elytra. 
The four posterior tibizw 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 are rather widely separated and the intercoxal 
process of the abdomen is obtusely rounded in front; in the 
male the coxe 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 T[listory Notes from H.M. Indian Marine 
Survey Steamer ‘Investigator,’ Commander Alfred Carpen- 
ter, L.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 
Acock, 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. 
Tur 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. This 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 Gult 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- 
eulla. 
