160 CEYLON PEARL OYSTER REPORT. 



Sense-organs. Eight sense-organs are present. The outer sensory pit is triangular 

 in outline and its surface is folded. The principal folds radiate outwards from the 

 bottom of the pit. The tentaculocyst is apparently without an ocellus, as there is no 

 trace of any pigment. The ocular lobes are much smaller than the velar lobes, and 

 are pointed. 



Sub-umbrella Muscles. In one specimen the sub-umbrella muscles have become 

 detached and a clear view of the canal system is obtained. In the other specimen 

 the muscles are present, and they form a circular band between the periphery of the 

 oral disc and the margin of the umbrella. The circular muscle band is continuous and 

 is not radially interrupted. 



Sub-genital Cavity. The four sub-genital ostia open into a common continuous 

 cavity. The ostia are very large, forming long but narrow slits, about 20 millims. in 

 width, and about as wide as the columns. The entrance is partly blocked in the 

 centre by a large triangular gelatinous knob on the sub-umbrella, and just inside 

 there is another median knob and also two small lateral ones. 



Oral Arms. In a normal specimen there should be eight oral arms of equal length, 

 but in both of these specimens the oral arms are abnormal in number and in length. 

 One specimen has ten oral arms, the four columns bearing respectively 2.2.3.3. arms. 

 The arms show a great difference in size, the largest is about 80 millims., and the 

 smallest about 25 millims. As one arm is much longer than the others, which are 

 all of different lengths, it is probable that the medusa received an injury in the oral 

 arms, and regeneration has followed. The upper arm is very short and is somewhat 

 laterally compressed. In the arm, measuring 80 millims. in length, the upper arm is 

 about 15 millims. and the lower arm about 65 millims. The lower arm has three thin 

 wings bearing oral mouths along the outer edges down to the distal end, which does 

 not bear a gelatinous knob. The oral mouths on the ventral wings are continued 

 along the upper arms to the oral disc, where they meet and form a cross-shaped 

 pattern. There are no special appendages of any kind upon the arms or the oral disc. 

 In the second specimen the arms are broken off close to the arm disc and there are 

 stumps of nine, possibly ten, arms. 



Stomach. The stomach is cross-shaped. The gastric filaments run round the 

 margin of the stomach and also curve downwards and inwards, forming a loop in the 

 base of the columns. It is at the end of the loop that the canal from the oral arm 

 enters the stomach. 



The gonads are immature. 



The specimens are of a whitish colour in formalin. 



So far as I can make out, these specimens belong to the genus Crambessa, but I am 

 not able to determine the species. As they are immature they are probably at an 

 intermediate stage in growth and may develop into a species which has already been 

 described. 



