CERATOSA KEY TO BRITISH GENERA 



are characterised by a granular ground substance and aphodal 

 chamber system ; the Spongelidae by a clear ground substance and 

 sac-like eurypylous chambers. 



The bath sponge, Eus^jongia officinalis, belongs to the Spongidae. 

 The finest varieties come from the Adriatic, the coarser ones from 

 the Dalmatian and North African coasts of the Mediterranean, 

 from the Grecian Archipelago, from the West Indies, and from 

 Australian seas. The softer species of the genus Hip2Jospongia 

 also form a source of somewhat inferior bath sponges. 



Among Dendroceratina, Dartvinella is unique and tempts to 

 speculation, in that it possesses isolated spongin elements, resemb- 

 ling in their forms triaxon spicules. 



Key to British Genera of Sponges. 



rSkeleton calcareous . . . . . .2 



I Skeleton siliceous . . . . . .6 



"I Skeleton horny, or -witliout free spicules . . .53 



(^Skeleton absent . . . . .55" 



I'Gastral layer continuous . . . . .3 



\ Gastral layer discontinuous, confined to chambers . . 4 



/'Equiangular triradiate systems present . . . Clathrina 



\Triradiate systems all alate .... Leucosolenia 



r Chambers tubular, radially arranged . . . .5 



1^ Chambers spherical, irregularly scattered . . Leucandra 



^ f Tufts of oxeate spicules at the ends of the chambers . Sycon 



(Oxeate spicules lying longitudinally in the cortex . Ute 



TAU the spicules hexradiate or spicules easily derived from hexradiate 



G I ^yv^ ' 



j Some of the spicules calthrops or triaenes . . .10 



[Megascleres uniaxial . . . . . .15 



., /"Amphidiscs present . . . . ' . .8 



\Amphidiscs absent . . . . .9 



(Rooting spicules a well-defined wisp ; four apertures lead into the 

 gastric cavity .... Hyalonema (homsoni 

 Rooting tuft diffuse ; sponge oval ; osculum single 

 Phcronema carpenteri 



[Sponge tubular, dermal and gastral piuuli alj.sent Eiipledella subei-ca 

 9. - Sponge a widely open cuj) ; dermal and gastral pinuli present 



[ Asconema setahalense 



i Tetractine spicule, a calthrop or triaene with short rhabdome ; 



10. - microsclere a spined microxea . . Dercitus hucklandi 



[Triaenes with fully developed rhabdome . . .11 



