388 HYALONEMA (SKIANEMA) UMBRACULUM. 



are 51-93 m long, usually about a third of the whole spicule, and 105-190 m broad. 

 The proportion of the length to the breadth of the anchors is 100 to 141-316, 

 on an average 100 : 225.3. The number of teeth in the anchor is from eight to 

 ten. The two anchors of the same spicule are usually composed of the same 

 number of teeth, and in this case the teeth of two anchors are generally regularly 

 alternate. Sometimes the number of teeth is not the same in the two anchors 

 of the same amphidisc, and in that case they of course do not alternate regularly. 

 The individual teeth arise nearly vertically from the ends of the shaft, and are 

 curved only slightly in their proximal half, but strongly in their distal half. This 

 curvature is so great, that the tips of the teeth become strongly convergent, and 

 the distance between the ends of opposite teeth is 12-32 ju less than the (maxi- 

 mum) breadth of the anchor. The outer band-shaped part of the tooth attains 

 its maximum breadth a little distance distally from the middle of its length, and 

 is here sometimes 32 ^ broad. At its distal end the tooth is simply rounded off. 



Besides these regular forms several irregular large macramphidiscs (Plate 101, 

 figs. 8-10) have been observed. In these spicules one or both of the terminal 

 anchors are irregular, and the shaft bears, besides the terminal anchor-teeth, 

 other protuberances which arise — usually in a verticil — from its middle-part. 

 All these supernumerary protuberances terminate at the (hypothetical) oval 

 wall of the amphidisc-cell, and are here abruptly bent or slightly extended to 

 terminal discs. 



The sviall macramphidiscs (Plate 102, figs. 3-6; Plate 103, figs. 24-26) are 

 78-128 fi long, most frequently about 112 /i. The shaft is straight, cylindrical, 

 smooth, and 6-11.5 m thick. The terminal anchors are 37-67 ^ long, about 

 half the whole spicule, and 53-104 n broad. The proportion of the length to the 

 breadth of the anchors is 100 to 138-176, on an average 100 : 150.6. The termi- 

 nal anchors consist of ten to thirteen teeth. The number of teeth is, as in the 

 large macramphidiscs, not always the same in the two anchors of the same 

 spicule. When it is the same the teeth of oppo.site anchors are usually situated 

 alternately; when it is not the same, there is no regular alternation of teeth. 

 The teeth arise nearly vertically from the ends of the shaft and are curved quite 

 uniformly, approximately through a quarter of a circle, to within a short distance 

 of the tip. The anchors are therefore nearly hemispherical in shape. The 

 outer band-shaped part of the tooth attains its maximum width of 15-20 ^ 

 some distance distally from the middle of its length. Sometimes its broadest 

 part lies quite close to the distal end, and in this case this end is broad and 

 rounded (Plate 102, fig. 3) ; sometimes it lies some distance from the end, and 



