96 Memoirs of the Indian Museum. [Vol. V, 



they were occasionally in September ; but this was not the case in those collected 

 between November and February. 



SCYPHOMEDUSAE. 



(Plate vi (in part) ; plate viii.) 



The only medusa of this group found in the Chilka Lake belongs to the order 

 Rhizostomata and the division Triptera. The species is here described as new and 

 belongs to a genus recently discovered in the Philippines, in which the only form 

 hitherto recognized occurs. The Chilka species is of considerable biological interest , 

 not only because it has been able to establish itself as a permanent resident in water 

 of very variable salinity, but also because we found it possible to estimate the direct 

 effect of fresh water upon the physiology of individuals (p. 101, postea). Some post- 

 larval forms were obtained and are here described briefly and figured ; they throw 

 light on the evolution of the Rhizostomatous mouth-arm. The species is also 

 common in the Bay of Bengal. 



Order BHIZOSTOMATA. 



Division RHIZOSTOMATA TRIPTERA. 

 Genus Acromitus, Light. 



1914. Acromitus, Light, Philippine Joum. Sei. (D) IX, p. 210. 



This genus has recently been described to contain a single species (A. maculosus, 

 Light) from the Philippines. Its most striking diagnostic character is the posses- 

 sion at the tip of each mouth-arm of a single greatly elongated tentacle-like filamen- 

 tous process. This process is very much longer and stouter than the small sensory 

 filaments scattered among the mouths on the arms. 



In describing a new species from the Chilka Lake and the Bay of Bengal I have 

 closely followed the descriptions of representatives of the order published in Meyer's 

 Medusae of the World (1910). In all the features accepted by Light (1914, op. cit.) as 

 of generic importance this species agrees with A. maculosus, the only other member 

 of the genus yet known. 



Acromitus rabanchatu l , sp. nov. 



(Plate vi, figs. 4-6; plate viii.) 



The disk is no flatter, at any rate in living medusae and in specimens recently 

 preserved in formalin, than a hemisphere. In large individuals its diameter is as 



1 Raban-chatu is the vernacular name given to this medusa by the Uriya fishermen of the Chilka 

 Lake, who would probably apply it also to any other medusa of similar shape. It means "the umbrella 

 of Ravana", the demon-king of Ceylon who plays the part of chief villain in the Ramayana. 



