KEY TO BRITISH GENERA 



223 



18. 



19. 



24. 

 25. 



26. 



27. 



28. 



29. 



30. 



31. 

 32. 



. 56 

 . 22 



Acarnus 



3 fonniiig tlie 



Plocaviia 



. 20 



Hamacantha 



Forcepia 



Hymeraphia 



Icqjhon 

 Pocillon 



. 28 

 . 30 



/'Habitat fresh Avater .... 

 ( Habitat marine .... 



Megascleres include cladotyles . 



Megascleres include dumb-bell or gausage-shaped spicule: 

 main reticulum .... 



]\Iicroscleres include bipocilli 



Microscleres include diancistra . 



]Megascleres include forceps 



Skeleton formed of isolated monactines vertically placed 



None of the above peculiarities jjresent 



('Skeleton fibre not echinated 

 (Skeleton fibre echinated 



(Skeleton with echinating spicules 

 (Skeleton without echinating spicules 



f Spongin abundant .... 



(Spongin scanty .... 



(Fibre not echinated .... 

 (Fibre echinated .... 



fFibre with a single axial series of spicules 



\ Fibres with numerous spicules arranged polyserially 



[Microscleres absent . . . , 



- IMicroscleres sigmata anclV 

 [Microscleres sigmata or / ' ' 



(Skeleton confused .... 



(Skeleton reticulate .... 



TEind and fistulous appendages present ; microscleres sigmata Oceanapia 

 -No rind; skeleton reticulate; microscleres sigmata and) n it 



(No rind ; skeleton reticulate ; microscleres sigmata or J * 



/"Skeleton confused or formed of bundles of spicules with echinating 



spined styles . . . .29 



^ Skeleton fibrous or reticulate, or formed of short columns . 45 



Skeleton formed of a dense central axis, and columns radiating from it 



I to the surface . . . . . .52 



[Spicules of the ectosome styles .... Pytheas 



■I Spicules of the ectosome oxeas or absent . . Clathrissa 



(Main skeleton confused. Special ectosomal skeleton absent Spanioplon 



TMegascleres of the choanosome not difl'ering from those of the 



. 23 



. 25 



. 24 



Liplodemia 



Chalina 

 Pachychalina 



. 26 



. 27 



Halichondria 

 Eeniera 



J ectosomi 



1 Megascleres of 



the clioanosome dilferiny from those 



( some 



fClielae absent . 

 I Chelae present 



fTrichodragmata present 

 (Trichodragmata alj.sent 



of th 



31 



ecto- 

 . 32 



. 33 



. 44 



Tedania, 

 . 42 



