146 



The Paragaster is deep ; it reaches nearly down to the point from which 

 the skeleton fibres (Skelet-radiant) radiate, and occupies about two- 

 thirds the entire height of the sponue. The exact point from which 



rig. 9. Aulacopella Winnipegensis. Vertical section through the middle of one of the 

 rays to the centre of the sponge. The fibres and canals of the skeleton partly re- 

 stored, though their course in the greater part of the original c^n be clearly followed. 



these fibres radiate could not indeed be actually observed, but its posi- 

 tion is so clearly indicated by the convergence of the fibres that the 

 possible deviation from its true position, as represented in the figure, 

 cannot amount to more than one or two millimetres. I have not been 

 able to find distinct inhalent canals, though it is possible that they may 

 have disappeared in consequence of the complete and unfavourable silioi- 

 fication* which the body skeleton has undergone. The basal surface 



* The rock is a most peculiar, very uniform, fine grained, siliceous limestone. The 

 grains, which for the most part measure from 30 to 60 micromillimetres, consist of well 

 defined calc spar rhomboids, which are so closely embedded in an isotropic siliceous 

 mass that the rock effervesces but weakly with acids, in spite of the amount of linje that 

 it contains. This sediment is completely free from other organisms, such as sponge 

 spicules, which are often found distributed throughout siliceous limestones. The whole 

 ailicified sponge body is free from calcareous matter, and is altered, not to an isotropic 

 silica, but into a compact cryptocryatalline chalcedony. 



