123 
5 . 
Skeleton of typically Re- 
nieroid structure in the 
erect forms: from the base 
rise primary fibres with 1 
—3 spicules side by side; 
they are radiating rather 
perpendiculary towards the 
surface; the distance be- 
tween them is ca. one spic- 
ula-length; hence there are 
more and more primary 
fibres towards the surface; 
new ones come up through 
intercalation or by fission of 
already existing ones. Se- 
condary fibres are not to be 
made out, they are only 
represented by single spic¬ 
ules connecting the prim¬ 
ary fibres, but not in cont- 
inuation of one another, 
or at least only in a few 
places and rather rarely; 
most of these spicules are connecting the primary fibres in pretty 
right angles. Around bigger cross-canals this fairly regular picture 
is disturbed. 
In the incrusting forms the skeleton is very irregular; only 
in a few places we recognize the above description of the struc¬ 
ture in the erect forms; the spicules are lying much more closely, 
the tissue contains more of them pr. cm*^ than in the erect forms; 
the irregular distribution is surely in the first place due to the 
faet that the canal system in the delicate incrusting sponge-body 
does not permit the regular formation of longitudinal diverging 
primary fibres. 
Spicules: (fig. 5) oxea of common regular form: slightly bent 
in the middle in a rather sharp curve, tapering at the last Vs into 
fine points. Length rather constant, 156 //, thickness 7,5 p. In a 
few specimens lengths down to 120 p are not quite uncommon. 
Fig. 4. Reniera heterofibrosa, Ldbck. Oxea. — 
Fig. 5. Reniera implexa, Schm. Oxea and apex 
of same. 
