502 " THETIS " SCIENTIFIC RESULTS. 



less coalesceiit and connected by transverse branchlets, thus form- 

 ing a subflabellate clathrous expansion. The branches are flat- 

 tened in the plane of branching, and measure from 5 to 15 mm. 

 in their greater and 3 to 4 mm. in their lesser diameter ; the 

 total height is 200 mm., and the greatest width about 60 mm.; 

 the peduncle is 40 mm. long and 5 mm. thick. The surface 

 generally is very rugose and marked by a series of sinuous 

 grooves and uneven knotty ridges ; near the summit of the 

 sponge the grooves and ridges become more regular and distinct. 

 The dermal layer of spicules is rather scanty and partly obscured 

 by the large smooth styli which project from the ends of the 

 fibres in great numbers and give the stem and branches an 

 extremely hispid appearance. The branches exhibit abundant 

 perforations ; these are situated in the grooves ; they are from 1 

 to 2 mm. in diameter and 2 or 3 mm. apart. By transmitted 

 light the sponge appears as if it had been riddled by small shot. 

 These perforations probably represent the oscula ; the ridges are 

 reticulated and minutely j)orous. 



Textui'e slightly compressible, but very tough ; colour greyish- 

 brown. 



The skeleton consists of a series of very stout, horny fibres ; 

 in the axial region they are from 0-4 to 0"5 mm. in diameter ; 

 occasionally some appear to have coalesced and measure from 0'7 

 mm. In the less dense portions of the axial plexus the primaries 

 are usually 2 or 3 mm. in diameter ; the secondaries are about 

 the same, but diminish to 1-5 or 1 mm. near the surface; the 

 connecting fibres are 1 mm. or less. The spicular core consists 

 of stout, smooth styli, with from 3 to 5 in ill-arranged rows ; 

 they are approximated at the base and more divergent at their 

 apices, especially at the terminal portions of the fibres. 



The echinating styli are unevenly distributed, being abundant 

 only on the secondaries, or the outer part of the primaries, 

 where they form the encircling margin of the larger pores. The 

 mesh centrally is oblong and about twice as long as broad ; 

 elsewhere it is more or less subquadrangular. 



Megascleres : — (1) Straight, gradually tapering, and entirely 

 spined styli ; size 0'08 to 0-1 by O-QOS mm. 



(2) Stout, curved, smooth styli; size 0'25 to 0-5 by 0015-0-018 ; 

 the latter occur in the fibres and project more than half their 

 length at their ends. 



(3) Straight, slender styli ; these form the dermal crust and are 

 also scattered throughout the sponge ; the base is often a little 

 swollen and tipped with a few minute spines ; the apex is long 

 and acute ; size 0-25 to 0-4 by 0-005 mm. 



Microscleres : — (1) Long, slender toxa, with a very slight bend 

 in the middle and straight shafts ; size 0-2 mm.; they occur 

 throughout the choanosome and often arranged in bundles. 



