156 
HYALONEMA (HYALONEMA) OBTUSUM. 
As above stated the sponge-body was in life obviously attached to a bundle 
of stalk-spicules, which have, however, been pulled out of it. Empty tubular 
spaces, sometimes 0.9 mm. wide (Plate 36 , fig. 26a), the walls of which are 
formed by fine, highly stainable membranes, mark the places where the upper 
ends of the largest of these stalk-spicules were situated. These spaces lie in the 
axial part of the sponge-body. They are conical, attenuated above, and extend 
upwards to within a distance of 2 mm. from the summit of the gastral cone. 
In the lower part of the sponge-body these spaces are surrounded by a kind of 
cement, composed of dense masses of stout, one- to five-rayed, most frequently 
tetractine or diactine acanthophores (Plate 36 , fig. 26). In this cement a 
few microhexactine-derivate pachyinicrohexactin.es also occur. Quite at the 
bottom, a short distance below the dermal membrane, numerous slender-rayed 
spicules with long spines, which I consider as slender acanthophores, form a 
kind of felt. These spicules are mostly tetractines, but a good many triactines 
and a few diactines, pentactines, and hexactines also occur among them. Transi- 
tional forms, connecting these spicules on the one hand with the stout acantho- 
phores above referred to, and on the other with the dermal pinules, are also found 
in this part of the sponge. 
The thin marginal part of the circular wall which surrounds the gastral 
cavity, and forms the boundary between the dermal and the gastral parts of the 
surface, contains numerous, longitudinally situated, diactine pinules, the distal 
rays of which protrude freely beyond the surface. 
The gastral surface, that is the surface of the gastral cone, and the inner 
surface of the wall surrounding the fissure-like gastral cavity are covered with 
micramphidiscs and gastral pinules. The micramphidiscs are situated irregu- 
larly, and in some places are so numerous as to form dense masses. The gastral 
micramphidisc-layer does not terminate at the openings of the efferent canal- 
stems into the gastral cavity, but is continued in the walls of these canals and 
their branches quite down into the innermost parts of the choanosome. The 
gastral pinules are mostly pentactine, but hexactine forms also occur. Their 
centres are 30-100 i± apart. Their lateral rays extend paratangentially in the 
gastral membrane; their distal apical rays arise vertically from the surface, and 
protrude freely beyond it, forming a dense fur about 125 m high (Plate 35 , figs. 1, 
3, 16). This pinule-fur is not, like the micramphidisc-layer, continued down the 
efferent canals, but terminates at their mouths. 
Small hypogastral pentactines, similar in position to the hypodermal pen- 
tactines above referred to, occur below the surface of the cone. 
