240 



KEY TO THE AUSTRALIAN GENERA. 



composed of pithed horny fibres without 

 foreign bodies, sometimes also withtriaxon 

 horny spicules, or without any skeleton at 

 all. Chambers large, oval, sac-shaped, or 

 branched. G-round-substance hyaline and 

 transparent. (Hexaceratina.) 6 



With a skeleton composed of tetract or monact 

 siliceous supporting-spicules, or rarely with- 

 er) "( out a skeleton, Microsclera, when present, 

 stellate or spiral. Chambers small, usually 

 spherical, rarely oval. Canals narrow. The 

 spicules are never cemented by spongin. 

 Sponges frequently corticate. (Chondro- 

 spongise.) (7), p. 241. 



With a supporting-skeleton composed of mon- 



axon siliceous spicules cemented by spongin, 



or of horny fibre with or without proper 



spicules or foreign bodies ; or of scattered 

 1 foreign bodies. Microsclera never stellate. 

 j Megasclera never tylostylote. Sponges 

 V. never corticate. (Cornacuspongisfi.) (8), p. 242. ' 



With triaxon horn-spicules. (Darwinellidse.) 



Without triaxon horn-spicules 9 



With horny fibres. (Aplysillidse,) 10 



Without skeleton. (Halisarcidse.) (11) 



With cells in the spongin-wall of the fibres . . lanthella, p. 22. 



Without cells in the spongin-wall of the fibres 12 



1^ Sponges lamellar, generally incrusting. Ske- 

 leton composed of numerous isolated slightly 

 ramified fibres Aplysilla, p. 26. 



(10) 



12 



< 



(11) 



Sponges erect, massive. Skeleton composed 

 of one or a few stout horny stems, from 

 which numerous branches originate Dendrilla, p. 27. 



Chambers regular sac-shaped ; subdermal 



cavity occupied by a network of trabecula) . Bajalus, p. 30. 



