32 LITHISTIDA. 



scarce: in the uppermost 5 railiiui. of the oscular tube or gastral cavity there 

 are no threads. 



Geographical Distbibution. — South coast of Australia : Port Pliillip 

 {Lendenfeld). 



3. Ordo CHONDROSPONGI^. 



Silicea, the ground-substance of which is hard and tough, like 

 cartilage. A cortex is often developed. The ciliated chambers 

 are spherical and small. The ground-substance is granular. A 

 supporting skeleton is nearly always developed*; it is composed 

 of tetraxou or monaxon siliceous spicules ; the latter are monact, 

 stylij or tylostyli. The spicules are never cemented by spongin ; 

 they form bundles, which are often regularly radially situated. 

 Microsclera often present, mostly polyact. 



This Order comprises the Corticates of Oscar Schmidt, together with the 

 Lithistidae and Gumminjc of the same author. It is composed of a portion of 

 the Myxospongia), all the Tetraxonia, and a portion of the Mouactinellida), as 

 conceived by Zittel. It differs from Vosmaer's Ordo SpiculispongijB only 

 by HaUsarca not being contained in it. 



Subordo TETRAXONIA. 



Chondrospongige with tetraxon spicules. 



1. Group LITHISTIDA; 



Body hard, with a central gastral cavity or with numerous vertical 

 tubes. Tetraxon, branched, irregular spicules present. Monaxon 

 megasclera and microsclera also occur. The spicules of the 

 supporting skeleton are mostly interwoven so as to form a 

 very dense skeleton. 



K.o specimens in the Australian Museum. 



* Chondrosia and Chondrilla are the only genera in which it is absent. 



