548 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



As mentioned above, the osculum is about 1 mm wide, so that 

 the tube appears contracted towards tbe osculum. 



Skeleton. (Plate XXXVIII., fig. 1.) 



The skeleton consists of compressed main fibres and a very regular 

 net work of connecting fibres of uniform diameter. 



The main fibres ai'e often expanded so as to appear flat, and then 

 the margins of the flattened expansions are perforated by oval holes 

 and in this way there is no abrupt distinction between main and 

 connecting fibres as they are connected by this intermediate 

 structure. 



The thickness of the main fibres where it is not expanded, is 

 0'066 mm. The main fibres are on an average 0"6 mm. apart, and 

 extend from the points of attachment of the sponge upwards and 

 outwards. They are disposed in a radiating manner round these 

 points to a certain extent. 



They are however very irregular, and much bent and curved in 

 various ways. 



They are cored with foreign siliceous spicules averaging a length 

 of 0-07-0 '09 mm. These spicules are always broken, and it appears 

 taken into the fibre without any discrimination. They protrude 

 to a certain extent beyond the surface of the fibre, causing it to 

 appear rough, or even spiny. The spicules are disposed mostly in 

 a longitudinal direction occasionally very oblique however. Then 

 one of their ends protrudes. This end is generally the more 

 pointed one of the two. Some of the spines thus disposed point 

 outward, towards the sui-face, others again inward towards the 

 centre of the sponge. The spicules are also, where they i)rotrude 

 entirely enclosed bya sheath of horny substance. (Plate XXXVIII., 

 fig. 1). 



The connecting fibres form a regular net-work. The meshes 

 average a diameter of 0-09 mm. 



The thickness of the connecting fibres is 0"025 mm. 



The connecting fibres contain in their axes similar foreign siliceous 

 spicules as the main fibres (Plate XXXVIII., fig. 2) these are 

 always disposed longitudinally. 



