BY R, VON LENDENFELD, PH.D. 495' 



The connecting fibres form a very regular network, where they 

 are of uniform thickness, but the otherwise regular meshes become 

 irregular when the thickness of the connecting fibres varies; in the 

 manner described above in the diagnosis of the sub-genus Irregularis. 



The network is more dense in the vicinity of the main fibres 

 than in the other parts. 



The connecting fibres are always free from foreign bodies. 



I. EUSPONGIA IRREGULARIS LUTEA. 



The main fibres are completely filled with foreign bodies About 

 70% sand grains and 30% broken foreign siliceous spicules. 



Their surface is rendered very uneven as the depressions between 

 the projecting parts of sand grains and spicules are not entirely 

 filled up with horny substance. 



The diameter of the main fi'>res is 0-05 mm. The knobs on the 

 surface may increase the thickness locally to 0*09 mm. The sand 

 gi-ains measure on an average 02 ram. ; and the siliceous spicules 

 attain occasionally a length of 0*1 mm. 



The meshes of the connecting fibres have an average width of 

 0*08 mm., near the main fibre and 0'2 mm., in the portions of the 

 skeleton which are more distant from them. The connecting fibres 

 are thicker in the vicinity of the main fibres. 



50% of the fibres are thick, with an average diameter of 0'02. 

 mm, 



40% of the fibres measure 0-01— 0-017 mm. 

 Thinner fibres are rare, the finest measure 0-005 mm. 



II. EuSPONGIA IRREGULARIS SILICATA. 



The main fibres contain a number df foreign bodies in their axial 

 poition. These are mainly siliceous spicules of other sponges. 

 Forming 90% of the foreign bodies. The other 10% are chiefly 

 foraminifera shells, &c., there is hardly any sand. 



