152 LUFFARIA. — APLTSIWA. 



The skeleton consists of main fibres and primary and secondary connecting- 

 fibres. The main fibres are knotty, 0*2 millim. thick, 1-5-2 millim. apart, and 

 cored with an axial string of sand-grains. The primary connecting-fibres are 

 0-067 millim. thick, and form by frequent anastomoses a network with poly- 

 gonal meshes, 0-6-1 millim. wide. The secondary connecting-fibres are 0-01 

 millim. thick, and form reticulations which occupy the meshes of the network 

 of the primaries. The meshes of this very fine reticulation formed by the 

 secondaries are polygonal, and only 0-16 millim. wide. Polejaeff gives a figure 

 of this network {loc. cit. pi. ix. fig. 5). The pith-cylinder in the primary con- 

 necting-fibres is about half as thick as the fibre. 



The surface is protected by abundant small sand-grains which are imbedded 

 in it. The inhalant pores are situated in groups of ten to twenty. The groups 

 are very distant ; there are only one or two such groups of inhalant pores in 

 each of the concave fields between the rounded and only slightly projecting 

 ridges which connect the conuli. The subdermal canal-system is very highly 

 developed. The subdermal cavity is continuous, O'5-l millim. wide, and 

 divided into separate compartments by fine membranes and slender trabeculsD, 

 which are spread out in it. The canals in the interior are very narrow. The 

 ground-substance contains abundant granules, and appears remarkably opaque 

 and untransparent. 



Polejaeff (loc. cit.) has described this sponge. I have re-examined his types, 

 and agree with him that the digitate and massive forms should not be described 

 as distinct varieties. 



Geogkaphical Distribution. — North coast of Australia : Torres Straits 

 {Macleaij) ; off Api, New Hebrides (' Challenger ') ; on reefs off Tahiti (' Chal- 

 lenger '). 



Genus APLYSINA. 



Spongidse with small ciliated chambers 0"025-0'035 millim. 

 wide, and a skeleton composed of a loose network of pithed fibres, 

 which are not clearly distinguished into main and connecting- 

 fibres. The surface is conulated, and not protected by a thick 

 cortex of sand. 



Aplysina spiculifera, n. sp. 



The sponge consists of a low incrusting mass, from the upper surface of 

 which large and irregular, somewhat club-shaped, digitate processes arise, 

 which attain a length of 100 millim., and a maximum thickness of 35 millim. 

 A large circular osculum is situated on or near the summit of each branch. 



