HEXACTINELLIDA. 11 



Possession Island, 384 m. (210 fms.) ; Voy. 'Challenger.' 

 Kerguelen Island, 274 m. (150 fms.) ; Voy. ' Challenger.' 

 East of Buenos Ayres, 1097 m. (600 fms.) ; Voy. ' Challenger.' 



EOSSELLA PODAGROSA. 



(Plate III., figs. 2, 3, and Plate V., figs, la-m.) 



Sponge cylindro-conic, broadest about the middle, with wide, oval, thin -edged 

 orifice, armed with upright marginalia ; the walls thick and firm, with a well-developed 

 root-tuft, composed of diactins and of oxypentactins of the same character as those of 

 the velum. With a velum about 5 cm. from the surface ; with buds of considerable 

 size, solidly attached to the parent by a broad base. The hypodermalia oxypentactins 

 with rough or smooth rays, without prickles. 



The calycocomes with relatively short primary rays ; discohexasters with long 

 secondary rays. 



There are ten specimens of this species, one of large size, four of medium size, 

 and five small ones, some of which are probably detached buds. All the larger and 

 three of the smallest specimens possess relatively large buds, with oscule and gastral 

 cavity, and fixed by a broad base ; compared with these, the buds on one of the 

 specimens of E. antarctica (see page 7) are very small, being only 2 mm. in 

 diameter, and detached from the main body, though still adherent to the pleuralia. 

 The largest specimen (PI. III., fig. 2) is 20 cm. in length, and 8-5 cm. in greatest 

 breadth ; the orifice is 2 • 5 X 2 cm. in diameter ; the walls attain a thickness of 

 2 • 5 cm. Two buds and the scar of a third are present on the outer wall. 



Beneath the fine, gauze-like dermal layer are seen the round openings of the 

 ostia from • 5 to 2 mm. in diameter. 



The diactin marginalia project about 1 • 8 cm. The root-tuft is about 3 * 5 cm. 

 in length. A few slender diactin pleuralia project a little above the general velar 

 surface. The gastral membrane, which forms a continuous, finely pilose layer, with a 

 sharply-defined circular rim a little below the edge of the orifice, roofs over the 

 openings of the postica with a fine, sieve-like network, the meshes of which are formed of 

 bundles of diactins covered with autogastral hexactins. In one specimen the lower part 

 of the gastral membrane is cavernous. In all but the smallest specimens the central 

 cavity is deep, but in the latter it only extends to half the length of the sponge body. 



The skeleton is mainly formed of bundles of diactins with a few large hexactins. 



The spicules. Principalia. The long diactins mostly smooth, or only very 

 faintly roughened near the ends, usually straight, tapering very gradually to slender, 

 sharp points, a large spicule being 8 • 25 x '054 mm. Hexactins of two kinds, either 

 regular with thickly spined rays, each 380 x lOju- (V. lb), or with the rays nearly 

 smooth, and with the odd pair of rays (each 1500 x 45jli) equal or unequal, and longer 

 than the other four (V. la). 



VOL. 111. 2 I 



