194 CEYLON PEARL OYSTER REPORT. 



Thyone (?) calcarea, a. sp. Plate L, figs. 17-20. 



One specimen from Cod Bay, Trincomalee (Stn. XXVII.), 6 fathoms. 



Length, 20 millims. 



The colour in spirit is yellowish-white. 



The tentacles are not present. 



The pedicels are small and numerous, and are the same colour as the skin. They 

 are scattered all over the body, and are more numerous on the ventral surface than 

 the dorsal. They form a double row on the five ambulacra, but only at the central 

 portion of the body. Those on the three rows of the trivium are longer and more 

 distinct than those of the two rows of the bivium. 



There are five small calcareous teeth. The integument is thin but fairly hard. 



The animal has a remarkably large calcareous ring, which is half the length of the 

 body. It consists of ten pieces, the five radials having posterior bifurcations which 

 are made up of a number of small pieces. Both radials and inter-radials are notched 

 anteriorly. The inter-radial pieces of the ring are not all of the same length (fig. 17). 



There is one Polian vesicle, 4 millims. long, and one madreporite. The gonads are 

 attached to the dorsal mesentery. The alimentary canal is much convoluted. 



Deposits : The spicules are numerous and overlapping. They consist of tables 

 only. These are irregular in shape, mostly triangular or polygonal, and have from 

 five to a dozen holes. The spire consists of two upright rods which join at the top 

 and terminate in one or two blunt points (figs. 18-20). 



As in the two previous species, the genus of this form, although probably Thyone, 

 cannot be decided with certainty because of the absence of the tentacles. 



Phyllophorus cebuensis (Semper) Plate II., figs. 22-24. 

 Thyonidium cebuense, Semper (2), 1868. See also Theel (7). 



One specimen from Gulf of Manaar (Stn. II.), 8-9 fathoms (see Note, p. 205). 



Length, 22 millims., and breadth, 13 millims. 



Colour in spirit : Brown epidermis covering a white skin. 



The mouth is slightly dorsal, so that the trivium is a little longer than the bivium. 



In the middle of the body the pedicels are irregularly scattered, being more 

 numerous on the trivium than on the bivium. At each end of the body, however, 

 the pedicels are arranged in five double rows. 



There are five small anal teeth. 



The calcareous ring agrees with Semper'*? description. Each of the radials has 

 four anterior processes, and also two posterior prolongations, each of which is made 

 up of four small pieces. The inter-radials are simple (fig. 24). 



Deposits : -Numerous tables of one kind only. Each table has a central hole 

 surrounded by about eight slightly smaller holes. The spire is tall and massive, and 

 consists of four upright rods, the adjacent ones being connected by four or five bars. 



