POEIPHORA. 3 



latter, what is the prevalent number of the rays ; 

 — are the principal points to be observed. 



Authorities. — Dr. Johnston's " History of British 

 Sponges " is far beyond any other yet published ; 

 and to it I am chiefly indebted for the following 

 arrangement. It is, however, imperfect ; and the 

 scientific world is expecting from the pen of Mr. 

 Bowerbank a revision of the Class, which his ex- 

 perience renders him more competent to give than 

 any other zoologist living. 



PORIPHORA. 



Bodies of various form, sometimes more or less 

 constant and regular, at others uncertain and 

 irregular ; always fixed ; composed of horny fibres, 

 or of spicula of lime or flint, endued with a glairy 

 coat of gelatinous granules, so arranged as to form 

 permeating canals, through which water is circu- 

 lated by the action of lining cilia. 



Tethea (Lamarck) . Solid and compact, rounded, 

 covered with a skin ; without sensible pores ; in- 

 terior fleshy, with spicula of flint arranged in 

 bundles, radiating from a central nucleus. 



T. cranium. Fig. 1. 

 lyncurium. 



