1885.] S. R. Ehon—Currenfs and Tides of the Hugli. 133 



Societies have been examined, and it is believed that the omissions will 

 prove to be of no great importance. I have added some species hitherto 

 recorded only from Singapore and Siam when their occurrence in India 

 is probable. Those acquainted with the order can alone appreciate 

 the labour involved and value it, a labour enhanced by the abso- 

 lute absence of any named collection in India. I have arranged as 

 far as possible the collection in the Indian Museum, Calcutta, and this will 

 always remain available for consultation by collectors. It is desirable, 

 however, that fresh eiforts should be made to increase that collection 

 which is particularly deficient in Bhynchota and does not possess one- 

 fourth of the named species. 



2. The Currents and Tides of the Hooghly and its littoral, and how 

 they are influenced. -^By S. R. Elson, Esq. 



About twenty miles, or more, to the eastward of the entrance channels 

 to the Mutlah River, and fifty to the eastward of the Hooghly River, 

 lies the northern end, or termination, of a peculiar deep gut of water, 

 named the ' Swatch of no Ground ' : where the delta sand-banks end so 

 very abruptly as to launch suddenly from seven into one hundred 

 fathoms, in the course of only three or four miles : and the depth is 

 300 fathoms at only 15 miles from the shore. 



This gut, if I may be allowed the expression, is, doubtless, the sub- 

 way, or aqueduct, for the conveyance, between the walls of the adjacent 

 raised sea bottom, of the cooler and dense briny current which, all 

 authorities show, runs up from S. W. to N. E. parallel with the Coro- 

 mandel Coast for at least eight months of the year,* and which con- 

 tinues onwards, as a sure convection current, towards the sun- warmed 

 shoal waters of the extensive submarine Ganges delta : thereby pre- 

 venting the river silt from settling so far seaward as it has done both east 

 and west of the head of the Swatch : even supposing that there is such a 

 great outpour of water from the northern rivers during the freshets as 

 some aver, but on which point there is, unquestionably, a doubt. 



At its head, the waters the Swatch pours forth seem to divide, the 

 main part running eastward towards Chittagong, and then down along 

 the Arracan Coast, at least so say some of the sea-directories. But a great 

 portion of this stream of water, and that which most concerns us, turns 

 westwards over the remarkably well-formed submarine sand dunes (alone 

 to be found to the westward of the Swatch of no Ground) stretching out 

 for more than thirty miles from dry land, and lying between the Bulchery 

 sand on the east and Balasore Roads on the west. In proof of which state- 

 ments, we have it from registers (kept on board the outer Light Vessels 



* See Blanford'B Rudiments of Physical Geography. 



