1907.] OF THE THIRD TANGANYIKA EXPEDITION. 253 



adherent, encrusting stones, in the substance of which they are 

 partly embedded ; also encrusting shells of molluscs ; tubes some- 

 times flat-sided. Tentacles about 20. Sessile statoblasts oval ; 

 floating statoblasts not observed. 



The appearance of this new PlumateUa is very difierent from 

 the European species and vai-ieties of the genus, as will be seen 

 by figs. 1 & 2, PI. XIY. 



The tubes form a thin, closely adherent, interlacing, encrusting 

 layer, and are partly embedded in the stone on which they grow ; 

 or, possibly, stony crystalline material has been deposited in 

 between and over the tubes. The tubes encrusting stones are 

 fairly tubular, but those encrusting moUuscan shells are flat-sided 

 or ea-shaped in section, and the adhering side has only a very 

 thin layer of chitinous material, so that the supporting shell is 

 used by the animal to form part of its protecting tube. The 

 tubes are of a light brown colour, clear and nearly transparent. 

 The raised ends of the tubes are always tubular and white. 

 Septa are present in the tubes at the points of branching. 



A full and well-extended head was not found ; but there is 

 every appeai'ance that the lophoj)hore is horseshoe-shaped, with 

 a.bout 20 tentacles. 



Sessile statoblasts wei-e found in the tubes (PI. XIV. figs. 3 & 4) ; 

 they are oval in shape, but varying a good deal in their pro- 

 portions of width to length, smooth, and surrounded by a thin, 

 narrow, flat annulus without air-cells ; their greatest size is : 

 length 450 p (Jy in.), width 343 ^t (-Jj in.). Ordinary floating 

 statoblasts with swimming annulus were not observed. 



Diameter of tubes 321 ^ (y^cr ii^-) on average. 



Hahitat. Encrusting stones just below water-level at Kalambo 

 and Kassanga ; and also encrusting shells in shallow water at 

 Chamkaluki. 



Plumatella repens, var. ? 



This specimen was found attached to shells of living Tiphobia^ 

 dredged from about 40 fathoms at Maswa. 



The tubes are brown in colour, semi-opaque, and show a 

 deposit of fine material in more or less regular longitudinal or 

 transverse lines ; they are partly adherent, branching irregularly, 

 tubular, and altogether have much I'esemblance to those of 

 Plumatella repens of our lakes and canals, from which it is hardly 

 possible to differentiate them. 



Fully extended specimens were not present, but the lophophore 

 appears to have about 22 to 24 tentacles. 



The diameter of the tubes is 364 j.i (^L in.) on average. 



Some sessile statoblasts found in the tubes are oval, smooth, 

 with thin flat annulus without air-cells, 407^ (-j^L in.) in length 

 and 278/^ (c^y in.) in width. Floating statoblasts with cellular 

 annulus were not observed. 



The tubes are larger, and the sessile statoblasts smaller and 

 more elongated, than in the preceding species. 



Proc. Zcol. Soc— 1907. No. XYIIP 18 



