310 CEYLON PEAKL OYSTER REPORT. 



Mantle transparent except for the muscle, bundles and the spicules. There is a 

 loose felt- work of fine spicules all over the surface, and the mantle is necked with 

 white on the siphons. There are four lines of white pigment dots down the inside of 

 each siphon (fig. 18). 



Branchial Sac with seven folds on each side, the most ventrally placed one on the 

 left side being very slight. The transverse vessels are of three sizes (fig. 7), in 

 the wider of which spicules are found. There are six internal bars on a fold, and the 

 meshes, between the folds, are square and contain about six stigmata. They are 

 crossed and sometimes interrupted by the third order of transverse vessel. 



Dorsal Lamina represented by moderate-sized triangular languets (fig. 17). 



Tentacles. About ten large, branched, with smaller ones between (figs. 10, 11). 

 Another specimen showed eleven larger and eleven smaller alternately placed, with 

 occasional still smaller ones (figs. 10, 1 1). 



Dorsal Tubercle large, hut simple ; horse-shoe shaped, with both ends turned in 

 (figs. 8, 9). One specimen showed, as an abnormality, a double tubercle (tig. 16). 



The Alimentary Canal forms a long open loop on the left side of the body. 



Gonads are present on both sides. Each is hermaphrodite, the spermatic caeca 

 being arranged around the masses of ova. 



Localities: (1) Alentura Paar, Station LV1IL, 26 fathoms, two specimens; (2) 

 Station I., otf Negombo, 12 to 20 fathoms, two specimens (of a reddish colour when 

 alive) ; (3) Station IV., off Karkopani, 6 to 9 fathoms, one specimen (l - 6 centims. 

 x 1*2 centims., with atrial siphons 6 millims. long, and very little sand); (4) Galle 

 Bay (from basket hung to a buoy), one specimen about 1 centim. long (the fixation 

 and growth must have taken place entirely between April 17 and May 9 ; 



(5) Station LIIL, 10 miles north of Cheval Paar, 7 to 8 fathoms, four specimens ; 



(6) Trincomalee, 11th February, one small specimen; (7) Aripu Reef, 18th March, 

 one small specimen. The two specimens from Alentura Paar are entered in our field- 

 notes as " Two transparent Cynthias with red edges to the siphons and sand on the 

 test." These two specimens were preserved in strong formol and are still very soft 

 and transparent. The inside of the test is in a gelatinous condition, is continuous 

 with the mantle, and adheres strongly to it round the anterior end. In dissecting, the 

 animal is as soft and gelatinous as when alive. 



A sandy Rhabdocynthia is a novelty, and if we consider the allied species of 

 Cynthia we find that this species differs from Cynthia arenosa, Hrdn., in the details 

 of the branchial sac and in the spicules and the dorsal tubercle. 



The spicules are of the usual Rhabdocynthia type, and are sufficiently illustrated 

 in the figures (figs. 12 to 15). 1 have considered the possibility of this form, the 

 largest specimen of which is only 2'5 centims. in length, being a young stage of 

 Rh. pallida (Heller) which attains a size of 9 centims. ; but there are in the collection 

 small specimens of the latter species measuring only 2 centims. across, and these have 

 already the characters of the adult and are entirely different from Rh. ceylouica of 



