158 CEYLON PEARL OYSTER REPORT. 



rest of the umbrella by a conspicuous circular furrow. Just below the circular 

 furrow the radial furrows begin. There are 16 deep radial furrows on the 

 ex-umbrella, one midway between every tentacle and sense organ, terminating at 

 the base of the marginal lobes. The bottom of each furrow is attached to the wall 

 of the sub-umbrella by a septum which divides the distal portion of the stomach 

 into 16 pouches (8 ocular and 8 tentacular). The septum is continued for a little 

 way down the middle of each marginal lobe, separating the prolongation of the 

 stomach in each lobe into two parts. But as the septum does not proceed along the 

 whole length of the gastric prolongation, two completely isolated pouches are not 

 formed. The whole of the ex-umbrella, including the marginal lobes, is closely 

 granulated. 



Tbe gastric filaments are arranged in four distinct groups, which are isolated from 

 each other by the four basal angles of the cross-shajjed mouth. There are about 10 

 to 12 filaments in each group arranged in a single row. Each group occupies the 

 whole space between the angles of the mouth. 



The mouth is large and cross-shaped, about 3 millims. in length and width. 



The gonads vary in shape, and, looked at from the sub-umbrella, appear circular or 

 oval. The largest are about 1 millim. in length and 0'75 millim. in width. Three 

 specimens in one bottle have rose-red gonads, and two in another bottle are of an 

 orange colour. All the specimens are in formalin. One is a male and four are 

 females with large ova. 



There are 16 marginal lobes, which are about as broad as long (2 millims.), and 

 have a rounded edge. Between these lobes are the eight tentacles and eight sense- 

 organs, which alternate with each other. The tentacles are of moderate length 

 (about 5 millims.), stiff, and taper to a fine point. The sense-organs have an otolithic 

 sac and a circular reddish pigmented ocellus. 



The collection contains five specimens, three of which are in splendid condition. Two 

 were from off Mutwal Island on March 19, and three from Muttuvaratu Paar on 

 March 29. The largest measures 9 millims. in width and 7 millims. in height. Two 

 specimens are 9 millims. in width and 5 millims. in height. The others are slightly 

 smaller. 



I have compared these specimens with Nausithoe punctata obtained from the 

 Zoological Laboratory at Naples, and feel certain that they belong to this species ; 

 in fact, they agree in every detail except in the shape of the ocellus. The Naples 

 specimens have a circular pigmented ocellus on a semi-circular or convex bulb, 

 whereas in the Ceylon specimens the ocellus forms a pigmented ring on a bulb with a 

 flat surface. 



The results obtained by the " Valdivia " and " Siboga " Expeditions show that 

 Nausithoe punctata has a very wide geographical distribution. It occurs in all the 

 oceans. It was taken by the "Valdivia" off the east coast of Ceylon, and by 

 Bigelow at the Maldives. 



