OONEMA. 307 



The micramphidiscs (Plate 60, figs. 16-23; Plate 62, figs. 12-14) are 15-40 /x 

 long, most frequently about 20 m- The shaft is cylindrical, straight or, very 

 rarely, slightly curved, and 0.7-1.7 fi thick. Sometimes it is slightly and gradu- 

 ally thickened near the middle up to 2 ^i; more frequently no trace of a central 

 thickening can be detected. The shaft is covered by blunt or truncate spines 

 about 0.5 M long. These spines are often very numerous. The anchors are 

 4-14 fx. 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 ij. 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, subgen. 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. 



