TUNICATA. 305 



Inspector of the Pearl Banks, Ceylon, and who was with me in the Gulf of Manaar 

 performing his last inspection in the spring of 1902 when these specimens were 

 collected. 



Ascidia depressiuscula, HELLER Plate II., figs. 10 to 22. 



Although I refer these specimens to HELLER'S species, I consider it desirable to give 

 a detailed account of them with figures, as HELLER'S description was brief and had no 

 illustrations of the internal structure. 



External Appearance. Body flattened, ovate in outline, attached by the whole of 

 the left side and posterior end. Apertures both on right side, on the anterior half of 

 the dorsal edge, small, not projecting. Right side of body rather depressed in centre 

 with more prominent rounded edges. Surface smooth ; colour (in spirit), grey, with 

 a slight brownish tinge. Size, 2 centims. x 1 centim. to 1*5 centims. x 3 millims. 

 to 5 millims. in thickness. 



Test cartilaginous, but rather thin, semi-transparent. 



Mantle with moderate siphons. The visceral mass on the left side is rather large. 



Branchial Sac having the meshes square or a little elongated transversely. All 

 the transverse vessels are very narrow, so that the ends of the adjacent rows of 

 stigmata are very close. Every eighth transverse vessel has, however, a wider 

 horizontal membrane than the intermediate seven. The stigmata are of moderate 

 size and about five or six to a mesh. The internal longitudinal bars are stout with 

 large knob-like papillae and occasionally smaller ones between (fig. 17) ; there are also 

 intermediate horizontal membranes crossing the meshes in places. 



Dorsal Lamina a plain membrane with slight, but distinct, transverse ribs and 

 small marginal denticulations (fig. 18). 



Tentacles numerous,' about 60 to 80, much the same size, with an occasional very 

 much smaller one (fig. 21). 



Dorsal Tubercle large, horse-shoe-shaped (figs. 19 and 20), with the opening 

 anterior and both horns coiled inwards. The nerve ganglion is placed close up under 

 the dorsal tubercle. The prebranchial zone is papillated. 



Alimentary Canal rather bulky, intestine wide, and full of fine mud (fig. 22). 



Gonads well developed. Vas deferens swollen. 



Localities : (1) Galle Bay, from a basket of pearl oysters attached to a buoy, seven 

 specimens; (2) Station LIV., north of Gulf of Manaar, depth 4 to 40 fathoms; one 

 specimen along with many Cynthiidae. 



The specimens from Galle are all very much alike in their characters, and figs. 10, 

 11 and 12 give the appearance and range in size. Fig. 14 shows the specimen from 

 the Gulf of Manaar, measuring 2 centims. x 1'5 centims. x 5 millims. 



The branchial sac of the Manaar specimen (fig. 15) differs a little from that of the 

 Galle specimens. It has the papillae relatively longer, the stigmata rather shorter, 

 and the meshes scjuarer. But as pieces of the branchial sacs from Galle differ a little 



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