212 ESPERELLA. 



The skeleton consists of a network of horny fibres, in which abundant longi- 

 tudinally disposed spicules are contained. These fibres form a network with 

 oval longitudinally-situated meshes. The fibres are, on an average, 0"12 millim. 

 thick, and the meshes 0*3 millim. wide. The spicules are so abundant in the 

 longitudinal main fibres as to render the horny substance hardly visible. In 

 the transverse connecting-fibres, however, which are of the same thickness as 

 the main fibres, the spicules are confined to the axial portion of the horny 

 fibre. These supporting spicules of the fibre-net are styli. They are, on an 

 average, 0-22 millim. long and 0-05 millim. thick, cylindrical and abruptly 

 pointed, the blunt end simply rounded off. They are often irregularly curved, 

 sometimes even S-shaped. In the ground-substance between the fibres, parti- 

 cularly just below the surface of the sponge, abundant scattered microsdera are 

 met with. These are of four kinds : — (1) spicules similar to those in the fibres ; 

 (2) diancistra, 0-2 millim. long and 0-009 millim. thick, with very sharp recurved 

 points ; these are rare and confined to the surface ; (3) irregularly curved 

 spicules which are pointed at each end, and which may be regarded as an 

 irregular form of toxea ; (4) chelae, 0-03 millim. long, with unequal ends. 



Esperella ridleyi, var. robusta, nov. 

 (Plate VI.) 



Stout dendritic sponges, which attain a height of 500 millim., attached by a 

 small base, from which the cylindrical, erect, simple branches arise. These 

 branches attain a thickness of 30 millim., and are terminally rounded ; they 

 consist of a reticulate structure. The sponge is exceedingly hard and 

 incompressible. 



Geogeaphical Distribution. — "West coast of Australia : Western Australia 

 (Baily). 



Esperella ridleyi, var. intermedia, nov. 



Incrusting sponges, from the upper side of which cylindrical erect processes 

 arise, which are on an average 25 millim. thick and attain a height of 200 

 millim. These processes ai*e generally slightly ramified, and consist of a 

 similar reticulate structure as those of the foregoing variety. 



The fibres of the skeleton are thinner than in E. r. robusta, and the spicules 

 are not so abundant in them. In consequence of this, the sponge is much 

 softer and more elastic. 



Geographical Distribution. — West coast of Australia : Western Australia 

 (Bailu). 



