10 mm, and more in length. In the dermal membrane wliicli rests on tlieir tan- 

 gential rays a secondary more regular skeleton-net with quadratic meshes, com- 

 posed of the tangential rays of similar but smaller spicules, is met with. In the 

 meshes of this network lie the incurrent pore-sieves. In a belt, 2 cm. wide, sur- 

 rounding the margin of the oscular sieve-plate the meshes of this network are 

 smaller than elsewhere. The dermal membrane is densely covered with piniiles. 

 The stout quadratic skeleton-net of the gastral membrane which forms the fiat 

 or slightly concave sieve-plate on the upper end of the sponge, is conspicuous by 

 its regularity. Also here the large meshes of the primary skeleton-net are occu- 

 pied by a secondary network of smaller mesh, whilst the surface is densely covered 

 with gastral pinules. This network is particularly clearly visible, the large 

 subgastral cavities and the excurrent canal-stems forming a dark background to 

 it. The subgastral cavity is not continuous, some of the membranes separating 

 the excurrent) canal-stems extend right down to the gastral membrane, i.e. the 

 oscular sieve-plate, and attach themselves to it. All the specimens are more or 

 less filled with fine clay-coloured silt and have the brownish-greenish-yellowish- 

 greyish colour characteristic of most Hexactinellida preserved in spirit. 



Longitudinal sections through the whole sponge show numerous irregular 

 lacunar cavities below the dermal membrane, from which canals of the diameter 

 of a little finger extend downward. Their width decreases towards the interior 

 and they are much branched. Between these incurrents the excurrents, which 

 join to form main canals of the thickness of a finger, extend. The latter open 

 into the irregular lacunar spaces extending below the gastral membrane, which 

 appears as an oscular sieve-plate. 



The supporting spicules of the interior are exclusively stout oxypentac- 

 tines. Their four basal rays lie in a plane and extend tangentially in the septa 

 dividing the incurrent and excurrent canals ; the apical ray pierces these septa 

 more or less vertically like a nail. These spicules are very variable in size ; the 

 largest attain a length of 15 mm. ; their rays are quite smooth and usually taper 

 gradually towards the sharp-pointed end. 



The prostaha marginalia protruding from the oscular margin, the long 

 prostalia basalia forming the root-tuft, and the large uncinates with very oblique 

 spines are also to be considered as macroscleres. The marginalia are 

 diactines, straight or slightly curved, 4-6 cm. long and 20-60 /^|thick. Their 

 distal parts are more slender than their proximal parts and terminally pointed 

 or slightly inflated. The proximal third, which is imbedded in the body of the 

 sponge, has a smooth surface; the distal, protruding two-thirds are usually 

 densely and uniformly covered with small, sharp, conuli-like tubercles so that 

 the surface appears shagreen-like. 



Between the proximal ends of these spicules and in other parts of the dermal 

 and gastral membranes uncinates, 2 mm. and more in length and up to 16 /* thick, 



