144 CEYLON PEARL OYSTER REPORT. 



Mouth with four lips and a siuuous margin. Four gonads extending over the outer 

 half of each radial canal. Tentacles 25 in number. One or two minute marginal 

 bulbs between every tivo tentacles. Sense-organs numerous, one or two, rarely three, 

 between every two tentacles, with a single otolith. Umbrella 15 millims. in 

 diameter." I clearly pointed out that I did not regard the thickening of the 

 umbrella as a definite peduncle, and consequently placed the species in the genus 

 Phialidium instead of in Irene. The result of the second examination, with specimens 

 of Irenopsis for a comparison, leaves no doubt that the thickening of the umbrella 

 must be regarded as a peduncle, so that the species does not belong to the genus 

 Phialidium. It resembles Irenopsis in the shape of the peduncle, in the position of 

 the gonads, in the number of tentacles, marginal bulbs and sense-organs. The basal 

 bulbs of the tentacles are slightly larger. But it has only four radial canals, four 

 gonads, and a mouth with four lips. If the specimen had been in this collection I 

 should certainly have considered it to be an abnormal Irenopsis, having four instead 

 of six radial canals. With four radial canals one would expect to see a mouth with 

 four lips. I think that Phialidium tenue had better be regarded as an abnormal 

 Irenopsis. 



Octocanna, Haeckel, 1879. 



Octocanna polynema (Haeckel) Plate II., figs. 8, 9, 10. 



Description. Umbrella about twice to three times as broad as high, and thick. 

 Stomach flat, octagonal base with eight lateral lobes, about 2 millims. in diameter. 

 Mouth with eight small lips. Eight radial canals. Gonads linear, extending over 

 the outer half of the radial canals and nearly reaching to the margin of the umbrella. 

 Sixteen tentacles. About three to four marginal bulbs between every two tentacles, 

 each having an excretory pore. One marginal sensory vesicle (seldom two) between 

 every two bulbs, each vesicle with two otoliths (rarely with one or three). 



Size : Umbrella up to 12 millims. in diameter. 



Locality: Palk Bay, one on March 16; off Mutwal Island, one on March 19; 

 Galle, one on August 25. 



Notes. The umbrella of two specimens is plano-convex in shape, fairly thick, and 

 its margin is curled inwards. The third specimen has a very thick umbrella, which 

 is more highly curved than those of the other two specimens, and the cavity of the 

 umbrella is very shallow. The stomach has eight lobes, from which run the radial 

 canals. The mouth is expanded in all the specimens and has eight small lips, 

 corresponding in position to the radial canals. The gonads, in two of the specimens, 

 are on the outer half of the radial canals, but in the third specimen they are more 

 central, occupying the central third of the radial canals. They are linear in shape, 

 increasing in thickness towards the distal end, and show fairly large ova. There are 

 eight tentacles in the smallest specimen (8 millims. in diameter), one opposite each 



