142 CEYLON PEARL OYSTER REPORT. 



organs as a better means of distinguishing between the two species. Irene ceylonensis 

 has only one sense-organ between every two tentacles, each sense-organ with a single 

 otolith. Irene palkensis has two to four sense-organs between every two tentacles, 

 and each sense-organ usually has two otoliths, occasionally three to four, and rarely 

 one. There is also a difference in the structure of the otoliths. 



Ireuopsis, Goette, 1886. 



Eucopidre with numerous sensory vesicles, and with numerous tentacles. Six gonads 

 in the course of six radial canals. Stomach upon a peduncle. 



Irenopsis hexanemalis, Goette, 1886. Plate I., fig. 4 ; Plate III., figs. 5 to 8. 



Irenopsis hexanemalis, Goette, 1886, p. 832; Chun, 189G, p. 5. 

 Phialidium tenue, Browne, 1901, p. 730, plate liv., fig. 4; plate Ivii., fig. 16. 



Description. Umbrella like an inverted basin in shape, with a flattened top, about 

 twice as broad as high. Velum narrow. Stomach short, with six lateral lobes, 

 situated upon a short, broad, cone-shaped or semi-globular peduncle. Mouth with 

 six lips, having a deeply-folded margin. Six radial canals. Gonads linear, on the 

 distal part of the radial canals, close to the margin of the umbrella. Tentacles, about 

 30 to 40. Marginal bulbs about three or more between every two tentacles. Excretory 

 pores opposite the basal and marginal bulbs. Sensory vesicles, usually one, sometimes 

 two, between every two bulbs, each vesicle containing a single otolith (occasionally 

 about two to four). Cirri absent. 



Size : Umbrella up to about 1 8 millims. in diameter. 



Locality : Palk Bay, 18 specimens on March 1G ; Cheval Paar, 9 specimens. 



Notes. The collection contains about two dozen specimens and nearly all are in 

 bad condition. The smallest is an intermediate stage measuring 5 millims. in diameter. 

 The stomach is situated upon a short peduncle which is about 2 millims. to 4 millims. 

 in length. The peduncle is variable in shape. In some specimens it is conspicuous, 

 but in others hardly noticeable. When semi-globular, or like a broad inverted cone, 

 it is quite recognisable. In some of the specimens the peduncle is flattened out 

 (whether this is natural or due to preservation I am unable to say), and in this 

 condition the roof of the sub-umbrella appears convex, and the top of the umbrella is 

 very thick. The stomach (fig. 8) is divided into six lobes, and its base seen aborally 

 is like a six-rayed star. It is very short, about 1 millim. in length, and about twice 

 as broad as long. The mouth has six conspicuous lips, which are continuous with the 

 lobes of the stomach, and the margin of the lips is deeply and closely indented with a 

 series of folds. In some specimens the stomach and its peduncle are within the cavity 

 of the sub-umbrella, but those specimens which have an extra thick umbrella may 

 have the stomach projecting a little way outside the cavity. 



