1915-] Fauna of the Chilka Lake : Coelenterates. 97 



much as 20 cm. The exutnbrella is smooth to the naked eye, but under the micros- 

 cope appears minutely granular, each granule consisting of a little prominence beset 

 with nematocysts. There are eight rhopalia, each flanked on either side by a small, 

 elongate, tapering marginal lappet. A furrowed exumbrellar pit extends inwards 

 down each rhopalium; as seen from above the outline of the pit is somewhat 

 expanded towards the margin and constricted inwards. The rhopalar lappets, which 

 are longer than the others, are not expanded inwards at the base and do not meet at 

 any point. The velar lappets, of which there are four pairs in each octant, are short 

 and broad; their tips are very broadly rounded or subtruncate, and the incisions 

 that separate them short, those separating the two lappets that form a pair being 

 shorter than those that separate one pair from another. There are thus 16 rhopalar 

 and 64 velar lappets, or 80 in all. 



The width of the arm-disk at its base is about two- thirds, and at the point at 

 which the arms originate from it about one-half that of the bell. 



There are four narrow genital ostia, each a little narrower than the pillar which 

 separates one ostium from the next. Each is constricted below by a thick, wide, 

 gelatinous process of the bell-disk, and a little distance outside each a broad triangular 

 process with a bluntly pointed tip is directed downwards and inwards from the 

 subumbrellar surface. It occupies a position immediately below one of the rhopalar 

 canals. The arm disk is very slightly emarginate in each perradius. The subgenital 

 cavity is broadly cruciform. 



At their bases the eight mouth-arms are joined together in a circle for a short dis- 

 tance. Their relative length is somewhat variable and one or more, perhaps owing to 

 accident, are sometimes shorter than the others; they are always comparatively long 

 in proportion to the vertical axis of the bell. The lower, bifid portion of each arm 

 occupies about four-fifths of its total length. In this region the mouths are arranged 

 in a single row down each margin of each edge of the three lamellae. On the upper, 

 simple part of the arm they extend up the inner edge, in the same formation, to its 

 point of origin. The fringed lips, however, are so contorted, and the minute capitate 

 stinging-tentacles so numerous upon them , that it is difficult to make out the precise 

 arrangement without studying immature medusae. Normally the arm is bluntly 

 pointed at the tip. 



The sensory filaments on the sides of the arms are short, slender and bluntly 

 pointed ; they are often entirely concealed among the capitate tentacles and seem 

 to be much better developed in some individuals than in others. Their arrangement 

 is not very regular, but, generally speaking, they are set in short transverse lines 

 parallel to and alternating with the mouths. The elongate terminal filament charac- 

 teristic of the genus is rather stout at the base and tapers gradually. When fully 

 formed it is of great length, but it is rarely well-developed on all the arms of an 

 individual and may be altogether absent from some. This is probably due to acci- 

 dent, for the tip of the arm itself is sometimes lacking. Not infrequently the fila- 

 ment has one or more short branches at its base. Possibly this is due to regeneration 

 after injury. 



