OONEMA. 
307 
The micramphidiscs (Plate 60, figs. 16-23; Plate 62, figs. 12-14) are 15-40 n 
long, most frequently about 20 n. The shaft is cylindrical, straight or, very 
rarely, slightly curved, and 0.7-1. 7 n thick. Sometimes it is slightly and gradu- 
ally thickened near the middle up to 2 ; more frequently no trace of a central 
thickening can be detected. The shaft is covered by blunt or truncate spines 
about 0.5 n long. These spines are often very numerous. The anchors are 
4-14 n long, usually a little less than a third of the whole spicule, and 5-12.5 m 
broad. The proportion of their length to their breadth is usually 100 to 68- 
130, rarely up to 100 : 156, on an average (of thirty calculated proportions) 
100 : 111.5. The larger micramphidiscs have relatively narrower (more slender) 
anchors than the smaller. In the micramphidiscs with anchors under 7.5 m 
in length the proportion of anchor-length to anchor-breadth is generally 100 to 
100-130, rarely up to 100 : 156, on an average 100 : 118.9. In the micramphi- 
discs with anchors over 7.5 m in length this proportion is 100 : 68-114, on an 
average 100 : 86.6. In consequence of the slenderness of their anchors the 
larger micramphidiscs appear as transitional forms connecting the smaller 
micramphidiscs with the smallest fimbriate amphidiscs. The individual anchor- 
teeth of the micramphidiscs are uniformly and considerably curved, concave 
to the shaft, in their basal part. Distally this curvature decreases and their 
end-parts are nearly straight. The total curvature is such that the (nearly 
straight) end-part of the teeth come to lie parallel or nearly parallel to the 
shaft and to each other. 
The above sponges differ from all the species of Hyalonematidae hitherto 
described by the anchor-teeth of their fimbriate amphidiscs bearing marginal 
frills. In some respects, particularly in respect to the basal anchors and the 
microhexactines, they resemble Hyalonema depressum F. E. Schulze. In respect 
to other characters, particularly in the various kinds of amphidiscs, they differ, 
however, fundamentally also from this sponge. 
OONEMA, eubgen. nov. 
Species of Hyalonema of which the amphidiscs of one of the kinds have 
relatively very large and broad, usually more or less semispherical, anchors 
about half of the whole spicule in length. 
The collection contains six specimens of this subgenus, which belong to 
five species, four of which are new. 
