192 CEYLON PEARL OYSTEE REPORT. 



The calcareous ring is, comparatively, of very large size, being 1 1 millims. long in 

 the smaller specimen. The posterior prolongations are composed of several smaller 

 pieces. 



The deposits consist of tables which are very thinly scattered. They have four 

 large central holes and also four smaller peripheral holes. In the larger of the two 

 specimens the tables are imperfect, the circumference being broken at several places 

 (Plate I., fig. 8). Whatever may have been the cause of this breaking up, there is 

 no doubt they were originally similar to those of the smaller specimen (fig. 7), which 

 agree with Theel's figure. 



There is no doubt that these specimens agree more closely with Theel's variety, 

 papuensis, than with the species. Thyonc fusus is a northern form, and Theel's 

 variety was obtained by the " Challenger " Expedition in Torres Straits. It is now 

 recorded from Ceylon for the first time. 



Thyone sacellus (Selenka) Plate I., figs. 9, 10. 



Stolus sacella, Sel. (1), 1867. Thyone rigida, Semper (2), 1868. Stereodenna Murrayi, 

 Bell (4), 1883. 



Two specimens from five miles off Negombo (Stn. I.), 12-20 fathoms, January 31, 

 1902. Lengths, 75 millims. and 50 millims. 



Colour in spirit -light yellow with irregular brown spots. 



The skin is hard and rigid. The tentacles are retracted. 



The pedicels are irregularly scattered over the body. They are very small and 

 numerous, showing an arrangement in three double rows on the trivium. These rows 

 are not continued to the extremities, but are confined to the middle of the body. 



The calcareous ring is typical of the species. 



Deposits : These consist of four-holed plates having on each side a half ring 

 arising from the centre of the plate at right angles (fig. 9). In addition to these I 

 find numerous plates having more than four holes and having short spines on the 

 surface (fig. 10). 



These specimens are evidently the same as Bell's Stereoderma murrayi, which is 

 now included in Selenka's species, Thyone sacellus. 



Distribution : Kurachee, East Coast of Africa, Torres Straits, Japan, and Ceylon. 



Thyone (?) fusca, n. sp. Plate I., figs. 11-13. 



One specimen from Back Bay, Trincomalee (Stn. XXI.), 8-12 fathoms; 18 millims. 

 long and 1 millims. broad. 



The colour of the spirit specimen is brown. The pedicels are the same colour as 

 the general integument. 



There are no tentacles present in the preserved specimen. 



The pedicels are irregularly scattered all over the body, being slightly more 

 crowded on the ventral surface than on the dorsal. There are no papillae present. 



