STEIiOSPO>"GIA. 173 



The skeleton consists of slightly compressed or cylindrical fascicles, about 

 1 millim. thick, which are 2-4 millim. apart and joined by a loose network. 

 The main fibres in the fascicles are 0-2 millim. thick, and cored with spicule- 

 fragments. The transverse fibres are on an average 0-08 millim. thick ; the 

 meshes rounded, square, or circular, 0-3 millim. wide. The connecting-fibres 

 are curved, 0-06-0-08 millim. thick, and anastomose to form a network with 

 irregular meshes, 1"2 millim. wide. 



G-EO&EAPHICAL DISTRIBUTION. — Indian Ocean : Zanzibar (Boston Society Coll., 

 Peahody Academy Coll.). 



Australian Seas {British Museum Coll.). East coast of Australia {Ramsay). 



Stelospongia costifera, Lamarck. 



Sponyia costifera, J. de Lamarck, Histoire des animaux sans vertebres, edit. 2, 

 torn. ii. p. 555 (1836). 



Large, very regularly cup-shaped sponges, attached by a broad, sometimes 

 perforated base, and broader than high. The walls of the cup are very regularly 

 convex, so that the whole sponge appears basket-like, semispherical. It attains 

 a height of 250 millim. and a width of 400 millim. The free margin is quite 

 continuous and circular, or oval. The wall of the cup is in large specimens 

 about 18 millim. thick ; it becomes slightly thinner towards the rounded 

 margin. The surface is covered with longitudinal ridges, which are more 

 marked on the outer side than on the inner. The ridges in the basal portion 

 of the outer side are very high and appear somewhat irregular, because tuft- 

 like excrescences arise from them. The adjacent tufts of different ridges 

 sometimes coalesce, and thus the whole structure is rendered very irregular. 

 Further up the tufts are smaller and more regularly situated in rows, 

 forming conspicuous ridges, which are at the margin about 6 millim. apart. 

 All the ridges appear serrated in consequence of the projection of small tufts 

 at regular intervals. The ridges on the inner side are, in skeletons, of uniform 

 character throughout, 5-8 millim. apart, 2-3 millim. broad, and raised only 

 slightly over the surface. Near the margin they run parallel to each other 

 longitudinally, and they do not anastomose in the marginal zone; further 

 down, however, they reticulate, forming a network with polygonal meshes, 

 which are 4-5 millim. wide and disposed in longitudinal rows. 



The living sponge is dark red, nearly black — a colour which is retained by 

 spirit-specimens. The dry skeleton is chestnut-brown, very stiff, shghtly com- 

 pressible, and elastic. 



The skeleton consists of longitudinally disposed fascicles, which extend per- 

 pendicularly to the surface, and which are connected by a loose network of 

 fibres. These bands are about 2 millim. thick and on an average 6 millim. apart ; 



