OF THE SPONGIADJ3. 255 



FIG. 



which the radii and the spherical centre are of 

 about equal length, while in the fully developed 

 sphero-stellate forms this graduation is never seen. 

 Pages 51, 52. 



165. SPHERO-STELLATE. X 660 linear. Having the radii 



acutely conical and based on a. large central sphere 

 of greater diameter than the length of the radii. 

 Tethea rohusta, Bowerbank, MS., a new species 

 from Australia, in the British Museum, presents an 

 excellent type of this form of spiculum. As the 

 central nucleus appears, under favorable circum- 

 stances, we distinctly trace a central canal in each 

 , ray, passing from the centre of the sphere to near 

 the distal termination of each of the radii, as re- 

 presented in Fig. 167. These canals are not 

 usually apparent in the perfect spicula, probably in 

 consequence of the fluid being hermetically sealed 

 within the canals of the radii, but I could not de- 

 termine the presence of the fluid by polarized light. 

 Pages 51, 52. 



166. SPHERO-STULLATE WITH CYLiNDRO-sueroLiATE RADII. 



X 400 linear. Having the cylindrical radii slightly 

 expanded and somewhat foliated at the distal ex- 

 tremities. This remarkable form was obtained by 

 washing some specimens of Oculina rosea from the 

 South Sea, and there is little doubt of its being 

 from an unknown species of Tethea. Page 52. 



167. A SPHERO-STELLATE SPICULUM, exhibiting the central 



canals in the radii. X 660 linear. Page 52. 



168.PiLEATED CYLINURO-STELLATE. X 660 linear. 



169. Having several recurved spines uniting and forming 



170. a pileus at the apex of the ray, shaped like that of 



171. a young mushroom. These singularly variable 

 spicula are abundant in Spongitta plumosa, Carter. 

 They are remarkable as affording a series of transi- 

 tional forms from a single straight spiculum to the 

 regular multiradiate stellate one. Fig. 168 repre- 



