SPONGES.— HALLMANIS . 



269 



much compressed lobe, together with the longitudinally bi- 

 sected stalk. 



It differs from O. axinelloides as described, chiefly in regard 

 to the situation of the 

 oscula, in the larger size, 

 and lesser abundance in 

 the fibres, of the principal 

 spicules, and in the much 

 greater development of the 

 superficial ("dermal") 

 skeleton. 



On casual inspection, 

 oscula appear to be ab- 

 sent ; but along the mar- 

 gin and one side of the 

 lobe are to be noticed, here 

 and there, light-coloured 

 rounded spots, 1.5 mm. or 

 less in diameter, which 

 prove to be concealed 

 oscula-like openings 

 covered only by a thin 

 membranous diaphragm 

 continuous with the (else- 

 where very thin and 

 scarcely discernible) der- 

 mal membrane. 



The "oscular mem- 

 branes" contain numerous 

 radially disposed horizon- 

 tally-lying auxiliary styli. 



Fig. 5S—0. axinelloides a Princi- 

 b Oxeote modifications of 



which are absent from P^ ^""^ 1 i- ^1,1 4.*„,„^\ 

 , rill same. Auxiliary stylus (unlettered), 



other parts of the dermal 



layer. A dermal skeleton 



proper can, therefore, 



hardly be said to be 



present. There is, however, a superficial skeleton of a special 



kind, formed of closely situated tufts of principal spicules ; 



these tufts, to the presence of which is due a minutely reticulate 



appearance of the surface, are borne upon extremely short 



fibres, or rather processes, which arise from the superficial 



transverse fibres. 



In the description of O. axinelloides the fibres are said to be 

 about 70 ]i thick and to be pretty abundantly cored by styli 

 about 100 X 8 /I in size. In the present specimen, the fibres 

 mav attain a diameter of 100 /<, and are sparsely cored — the 



