302 CEYLON PEARL OYSTER REPORT. 



edges of the opening, smooth on the posterior half of the body. Colour a translucent 

 pinkish grey, or sometimes grey-green, rather redder on the anterior end and 

 especially on the siphons which are bordered with yellowish green. Size, 17 centims. 

 x I '2 centims. x 1 centim. 



Test of a soft cartilaginous consistency, semi-transparent, echinated around the 

 anterior end, smooth posteriorly, with an occasional little tubercle ; a few small shell 

 fragments adhering to test near area of attachment. 



Mantle with five pyriform muscle masses on each side ; the one set run towards the 

 atrial siphon (fig. 28) and the other set towards the branchial. In addition to these 

 there are finer bundles and the siphons are strongly muscular (fig. 29), having both 

 longitudinal and transverse bands of considerable bulk. 



Branchial Sac with wide, regular, rounded stigmata arranged two (rarely three) in 

 a mesh (fig. 30). The transverse vessels are all of one size. The internal bars are 

 narrow and have short papillae. Along the dorsal edge of the sac the internal bars 

 are imperfect, the branches arising from the transverse vessels forming triradiate 

 processes (fig. 31) which do not meet across the mesh to form a bar. 



Dorsal Lamina a series of long narrow pointed languets (fig. 32). 



Tentacles of three sizes, closely placed ; about sixteen of each of the two larger 

 sizes and about double that number of very much smaller ones. 



Dorsal Tubercle deeply crescentic, the horns pointing towards one another across 

 the opening (fig. 33). 



Localities: (1) Palk Bay, March 16, trawling, one specimen 17 centims. long, 

 and one 8 millims. long; (2) Gulf of Manaar, adhering to a fragment of a large 

 chank shell, 10 fathoms, 2 specimens, also on coral fragments ; (3) off Mount Lavinia, 

 Station XL VI., 30 fathoms, one specimen in a crevice on coral mass, " pale grey-green, 

 apertures bordered with yellowish green." 



It is not easy to say whether the specimens of Rhodosoma from Ceylon can be 

 safely identified with any of the species already named (we can scarcely say 

 ' known"). In 1855 STIMPSON very briefly described two species, Schizascus 

 pellucidits and S. papillosus, both from China, which seem to differ so little, if we 

 may judge from the published descriptions, that they may well be one species 

 belonging to the genus Rhodosoma of EHRENBERG (1828); but not to EHRENBERG'S 

 species R.'verecundum. In 1878 HELLER described, almost equally briefly, Rhodo- 

 soma seminudum from Jamaica, and gave a figure of the exterior which, however, 

 shows no very distinctive features; so much so that TRAUSTEDT, in 1882, describing 

 specimens of the genus from the same neighbourhood (West Indies), hesitated to 

 refer them to HELLER'S species, and gave them the name Rhodosoma pyxis, followed 

 by a detailed description. He distinguished this species clearly from R. callense 

 (LAO. DUTH.), the only other sufficiently described form. SLUITER, however, in 1898, 

 took a different view and refused to share TRAUSTEDT'S doubts. He appropriates 

 TRAUSTKDT'S accurate anatomical description to HELLER'S diagnosis of R. seminudum, 





