HYALONEMA (HYALONEMA) PLACUNA. 
219 
the whole spicule, and 5-11 m broad. The proportion of their length to their 
breadth is 100 : 58-92, on an average 100 : 73.8. The teeth arise nearly vertically 
from the shaft, and are strongly curved in their proximal part. Their distal 
part is straight, or only slightly curved, concave to the shaft. Their end-parts 
usually diverge slightly from the shaft, sometimes they are parallel to it. 
In form A these spicules (Plate 63 , figs. 43-45; Plate 64 , figs. 14, 15) are 
similar. Their dimensions are here: — total length 21-34.5 most frequently 
25-33 tx) anchor-length 7-12.5 anchor-breadth 5-9 u', proportion of anchor- 
length to anchor-breadth 100 to 56-100, on an average 100 : 71.7. 
Tetradisc. In form B I found a tetractine (stauractine) spicule (Plate 63 , 
fig. 51) with irregular terminal anchors on three of the rays. The fourth ray is 
broken off. The four main-rays of this spicule are densely spined, and the 
straight ends of the anchor-teeth, particularly of the longest, also bear conspicu- 
ous spines on their inner side. This spicule has a total diameter of 87 m- The 
anchors are about 35 m long and 36 m broad. 
The above description shows that these two sponges differ from each other 
in respect to the shape and size of several of their spicules, particularly their 
dermal and gastral pinules. These differences are cjuite constant and striking. 
I do not, however, consider these differences sufficient for specific or varietal dis- 
tinction. I therefore place the two sponges in the same species and distinguish 
for them, within this species, two forms. 
There can of course be no doubt about this species belonging to the Hexac- 
tinellida Amphidiscophora. It is more difficult to determine the genus, as 
the remarkable shape indicates a new generic character. Since, however, the 
specimens on which it is based are somewhat fragmentary, and since no trace of a 
stalk or other supporting apparatus is present, I refrain from doing so and place 
it provisionally in the genus Hyalonema, subgenus Hyalonema, some of the known 
species of which are quite similar in respect to spiculation. 
These sponges are distinguished by their shape and the dimensions of their 
spicules to such an extent that they can not be assigned to any of the described 
species. Their nearest allies are Hyalonema (H.) tenuifusum and H. (H.) tylo- 
stylum. From these they differ by the presence of protruding ridges (folds) which 
are absent in the two last named species; also by the dermal pinules being 
smaller and having much shorter lateral rays than in H. ( H .) tenuifusum (the 
dermal pinules are larger than those of II . ( H .) tylostylum ); by their gastral 
pinules having longer distal rays than in H. (H.) tenuifusum (the gastral pin- 
ules are larger than those of H. (H.) tylostylum) ; by the microhexactines being 
