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 a\'erage 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 m; anchor-length 7-12.5 m; anchor-breadth 5-9 yu; 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 /<• The 

 anchors are about 35 ^ long and 36 ^ 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 quite 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 Ainphidiscophora. 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.) 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 H. (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 



