20 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). 



Genus. Ceratella. (Gray.) 



Colony irregularly branching ; more or less expanded in one plane ; growing 

 from a creeping base. Main stem flattened, branches rounded and beset with 

 bracket-like hydrophores. 



(2.) Ceratella fnscn. (Gray.) 



Colony branching and fan-shaped ; expanded in the one plane ; erect. Skeleton 

 consisting of a light or dark-brown chitinous network ; the main stem broad and 

 flattened ; brandies numerous with the bracket-shaped hydrophores nrranged on 

 them in a roughly spiral manner and formed of ribs continuous with the fibres of the 

 stem and united by thin perforated lamina; the ribs projecting at the outer margin. 

 All the spaces within the chitinous network filled by a much branching hydrophyton 

 and the whole enclosed by an external layer of ectoderm. Gastrozooids seated on 

 the hydrophores, erect, with capitate tentacles irregularly scattered (10-14). 

 Gonophores medusoid, fixed. 



Localities. Coogee, Bondi (N.S.W.), Broughton Island, Flinders Island, Lord 

 Howe Island. 



(3.) Ceratella procnmbcns. (Carter*). 



Colony procumbent, thickly branched on the same plane ; the larger stems 

 chiefly on one (the lower) side, hard, flexible, of an ochre-brown colour, tinged here 

 and there with purple. Trunk short, solid, compact, compressed vertically, soon 

 dividing irregularly or subdichotomously into round branches which are confined to 

 the lower surface, ending in branchlets with sub-clavate ends, that appear on the 

 upper or opposite side, not reuniting or anastomosing. Hydrophores consisting of 

 a little semitubular plate, extending outwards and forwards from the side of the stem 

 on the proximal border of an aperture in the latter; scattered thickly over all the 

 branches, but most prominent on the branchlets ; frequently represented by the little 

 hole alone in the stem where the projecting portion lias been worn off; scanty on the 

 lower side of the main stems. Minute structure ; composed of clathrate chitinous 

 fibre throughout, whose meshes are subrectangular ; hydrophore formed of the 

 semitubular scoop-like plate mentioned supported on its proximal side by an extension 

 of the clathrate structure of the stem and bordering the little hole also above 

 mentioned, which extends into the centre of the stem ; surface of the larger stems 

 bluntly microspined. Size of largest specimens 11 inches long by 5 inches broad, 

 and about 1 inch thick or vertically. 



Locality. Cape of Good Hope, Natal. 



* Ann. and Mag. Nat. Hist., 1873. Transformation of an entire shell into chitinous structure by the Polype 

 Hydractinin, with short descriptions of the Polypidoms of five other species (PI. 1). The descriptions of G. procumbens, 

 C. spinosa and Clatina ericopsis are taken with only slight alterations from this paper. 



