g8 Memoirs of the Indian Museum. [Vol. V, 



The stomach is cruciform. There are eight rhopalar and eight adradial canals. 

 The former reach the broad zone of anastomosing circular canals externally, but the 

 latter are usually separated therefrom by an inwardly projecting portion of this peri- 

 pheral system. Even in adult medusae an adradial canal can sometimes be traced in 

 a straight line through this projecting portion to the outer zone, but more frequently 

 it loses its identity on entering the former. The gastric filaments are numerous but 

 very small. They are short, cylindrical and bluntly pointed. 



The colour of the bell, arm-disk and arms is milky white, neither transparent nor 

 altogether opaque. As a rule the bell is ornamented with dark spots, but their size, 

 number and arrangement are variable, and often they are absent. Sometimes 

 (perhaps most frequently) there is a broad immaculate peripheral zone and the spots, 

 which are about 2 mm. in diameter, are densely scattered over the remainder of the 

 bell; but sometimes they extend outwards to the marginal lappets, and I have seen 

 medusae, apparently quite uninjured, in which there were only some half a dozen 

 minute specks on the central part of the dome. Sometimes the spots are rather 

 large and fewer than usual; I have examined one individual in which they ran 

 together to form large irregular blotches on the margin. The pigment appears, in 

 the living medusa, almost black to the naked eye, but if the animal is allowed to die 

 in water it streams out in a deep purple cloud. In spirit or formalin the spots fade 

 to a reddish brown and gradually, after some months, disappear altogether. The 

 gastric filaments and the gonads are naturally of a yellowish flesh-colour, but fade 

 immediately to opaque white in spirit or formalin. 



Type. — No. Z.E.V. 6740/7, Ind. Mus. Preserved in 5 % formol. 



Distribution. — This medusa is common in shallow water on both sides of the Bay 

 of Bengal and in backwaters in the Madras Presidency. I have examined specimens 

 from the coast of Tenasserim and of Orissa. In the Chilka Lake it occurs at all 

 times of the year both in the outer channel and in the main area. We found it in 

 water of every degree of salinity up to that normal in the Bay of Bengal, and even in 

 pure fresh water ; it evidently breeds in brackish water. The effect of fresh water 

 upon it is discussed below (p. 101). 



Acromitus rabanchatu is closely allied to the type-species of the genus {A. macu- 

 losus, Light 1 ), from which it differs in colouration, in having the velar lappets shorter 

 and blunter than the rhopalar, the terminal arm-filaments stout and tapering at the 

 base, in the shape of the rhopalar pits and rhopalar lappets and in several other 

 minor characters. 



Young stages. 



Many small specimens were obtained in tow-nets, especially in November, 1914 

 in the immediate neighbourhood of Barkuda Id. The smallest are about 3 mm. in 

 diameter and represent an interesting stage in the development of the species. 

 Practically every other stage up to the full-grown medusa is represented in our 

 collection. 



1 Philippine lourn. Sei. (D) IX, No. 3, pp. 210-216, figs. 4-6 (1914). 



