1915-] Fauna of the Chilka Lake ; Coelenterates. 113 



Type. — No. Z.E.V. 6643/7, Ind. Mus. The specimen belongs to the bushy 

 phase and was taken in a canal of brackish water on the outskirts of Calcutta. 



Bimeria fluminalis is common in both phases in canals, creeks, pools and back- 

 waters of brackish water in the Gangetic delta. In the Chilka Lake the dwarfed 

 form is abundant, especially in the main area, at all seasons. 



The species is closely allied to Bimeria vestita, Wright, the type of its genus, 

 which occurs in the North Sea and Irish Channel and in the Mediterranean and has 

 been recorded from the Pacific side of South America. 1 



From the British form it differs only, so far as the hydrophyton is concerned, in 

 the more obscure annulation of the stems and the thinner and less conspicuous cover- 

 ing of the base of the hydranth and the tentacles. The cup-like invagination 

 produced at the base of the contracted hydranth is doubtless correlated with the 

 latter feature and is certainly not a generic character. Until I was acquainted with 

 the structure of the gonophore in both sexes I was of the opinion (see Faun. Brit. 

 Ind., Freshw. Sponges, etc., p. 140; 1911) that the Indian hydroid was at most a 

 local race of the British one, but the spadix differs in the two, for in the male of 

 B. vestita (fide Allman) it is branched instead of being simply cylindrical, while in the 

 female,' 2 instead of forming a cylindrical process 'on one side of the ovum, it forms a 

 symmetrical cup in which the ovum rests. 



B. fluminalis plays much the same part in the aquatic fauna of the Gangetic 

 delta as Cordylophora lacustris does in that of the estuarine tracts at the mouths 

 of the Thames and the Mersey. It reaches its maximum development on 

 submerged timber and there provides a support or a refuge to numerous fixed and 

 free Protozoa, while the Indian race or species (bengalensis) of the Polyzoon Victorella 

 grows on its branches just as V. pavida does on those of Cordylophora mUngland. In 

 the Chilka Lake the dwarfed form of the hydroid is found on rocks and stones and on 

 the stems of water-plants, avoiding only those spots reached by direct sunshine. 

 On stones it is confined to the lower surface, but on rocks it often covers vertical 

 faces. In the Gangetic delta, where there are no stones, this form is usually found 

 on hard artificial objects such as bricks and potsherds but also grows on water- 

 plants in pools. I have never seen the species in places where the water was perma- 

 nently fresh, but it flourishes in a medium of very slight salinity and can exist for a 

 considerable period in fresh water. The positions it affects in the Chilka Lake are for 

 the most part the same as those affected by Laxosuberites lacustris, except that, 

 when the lake is full, it grows higher up the rocks than the sponge. The rhizome 

 is very often completely buried in the sponge, through which the branches protrude. 

 In these circumstances the hydroid is more completely dwarfed as a general rule 

 than it is when growing free ; often the hydranths die and the branches disintegrate, 

 leaving only the rhizome, which retains its vitality and doubtless produces new stems 

 if anything happens to the sponge. 



1 Hartlaub, Zool. lahrb., Suppl. VI, p. 534 (1905). 



2 I can find no published description of the female gonophore of B. vestita. My statement is based 

 on a specimen from Port Erin that Mr. F. H. Gravely has kindly lent me. 



