46 TETIITOPSILLA. TRTTIYA. 



all over the surface. — (B) Elastic Variety : the head bears only one or two very 

 short and much curved, pointed, tangential rays. The head is bent down and 

 immersed in the surface, like the proximal end of the radial ray, but not so firmly. 

 The radial ray is hereby completely curved round, and forms a semicircle. The 

 slightest touch is sufficient to liberate the head of the spicule, which then, in 

 consequence of the vertical insertion and elasticity of the radial I'ay, is thrown 

 out with great force. These elastic defensive spicules appear analogous to the 

 cnidoblasts of the Cnidaria. 



G-EOGEAPiiiCAL DISTRIBUTION, — East coast of Australia : Port Jackson 

 {Lendenfeld). 



Mauritius (ILtnst). 



Subordo MONAXONIA. 

 Chondrospongise with monaxon niegasclera, styli and tylostyli. 



Eamilia TETHYD^. 



Spherical Monaxonia with regular sulidermal cavities between 

 the distal ends of the radial spicnle-bnndles. 



Genus TETHYA. 

 'J'etliydiD with stellate microsclera. 



Tethya multistella, u. sp. 



I distinguish two A^arieties of this species — megasteJJa and microstella. 



Spherical sponges, 20-40 millim. in diameter, attached by a small base, or 

 also by half the surface ; in the latter case the specimens attain a more semi- 

 spherical shape. Surface regularly tuberculose. The tubercles are divided from 

 each other by a network of depressions, which occasionally appear as sharp 

 lines (transition-form to Tethya fissurata), but more often have the appearance 

 of simple and undefined concavities. The tubercles are raised l*5-2'5 millim. 

 above the depressions, and represent the terminations of the spicule-bundles. 

 Light red, flesh-, or rose-coloured in the living state ; if properly preserved 

 tlie colour is retained in spirit without much alteration : badly preserved 

 specimens are culourl(\ss. \A'liitc. The ititcn'icn' is always dirty white : the 



