TUNICATA. 311 



corresponding size. It differs from Rhabdocynthia tenuis, HRDN., in the external 

 appearance and in the dorsal tubercle. 



Microcosmus manaarensis, n. sp. Plate II., figs. 23 to 31. 



External Appearance. A rough mass of sand, foraminifera, and shell fragments, 

 stiff but brittle, with more or less of the anterior end and two short siphons 

 projecting, and having the posterior end thickly covered and prolonged into root-like 

 sandy wisps (figs. 23, 24). Size about 2 centims. in diameter ; colour varying with 

 the sand. The siphons may be echinated with slight projections. 



Test white in section, leathery, but more or less completely buried in the crust of 

 sand, which may extend to nearly 1 centim. in thickness. The inside of the test is 

 quite firm and glistening, and is marked by the impress of the strong muscle bundles 

 of the mantle. The outside of the test bears numerous hair-like processes which run 

 out into the sandy coating (fig. 25). 



Mantle yellowish brown and very strong. The siphons are long and muscular 

 (fig. 28). Atrial aperture bilobed on inside (fig. 27). 



Branchial Sac with six folds on each side. There are five bars on a fold and 

 three in the interspace. The meshes are elongated transversely and contain about 

 10 stigmata. There are seven narrower transverse vessels between each pair of very 

 much wider ; narrow horizontal membranes cross some meshes (fig. 31). 



Dorsal Lamina a plain membrane. 



Tentacles six large and six smaller alternately, much branched (fig. 29). 



Dorsal Tubercle small, cordate in outline, with the opening anterior and both horns 

 turned in (fig. 30). 



The peripharyngeal bands have a characteristic undulating course. 



Localities : (l) Station LIIL, 10 miles north of Cheval Paar, 7 to 8 fathoms, two 

 specimens which differ in the amount of sand they bear; (2) Station XL VI., off 

 Mount Lavinia, 30 fathoms, two specimens ; (3) " Gulf of Manaar," three specimens ; 

 (4) Trincomalee, Station XXIV., 30 fathoms, three specimens. 



This species differs from those already known from eastern seas, such as M. helleri, 

 M. ternatanus, M. propinquus, M. affinis, and M. ramsayi, and also from the two 

 new species found by the " Siboga" expedition, M. harniisphcerium and M. arenaceus. 

 The last-named species is a sand-covered form like the present one, but differs notably 

 in the dorsal tubercle, which is broken up into several separate openings, and in 

 having papillae on the horizontal membranes at each longitudinal vessel. 



The species to which the present seems most nearly allied is M. gleba, TRAUSTEDT, 

 from the Pacific; a species which differs in having 10 large tentacles and in some 

 details of the branchial sac. 



This species forms dark sandy balls about the size of a walnut, and in most 

 specimens the fringe of sandy rootlets at the posterior end is conspicuous (fig. 23). 



The coating of sand is so thick and dense that in some cases it can be peeled off 



