216 HYALONEMA (HYALONEMA) PLACUNA. 



transverse diameter. The end-breadth is 6-9 m less than the maximum breadtli. 

 The proportion of the length to the maximum breadth of the anchors is 100 to 

 72-107, on an average 100:87.0. There are usually about ten teeth in the 

 anchor. The teeth arise nearly vertically from the shaft and are curved rather 

 strongly in their proximal part; distally their curvature decreases. Altogether 

 it is such that the ends of the teeth converge towards the shaft, with the axis of 

 which they enclose angles of about 7°. The teeth are T-shaped in transverse 

 section. The distal band-shaped part, which corresponds to the horizontal 

 stroke of the T, is uniformly about 12 /j. broad for the greater part of its length, 

 and very blunt-pointed or rounded at the end. 



The dimensions of the single spicule of this kind found in form A are; — 

 length 315 ju; thickness of shaft 7yu; anchor-length 90 /u; maximum anchor- 

 breadth 95 yu; proportion of anchor-length to maximum anchor-breadth 100 : 100. 

 The small macramphidiscs with apically narrow anchors of form B (Plate 65, 

 fig. 1) are 296-319 n, most frequently about 308 fi long, have a shaft 0-8.5 ^ thick, 

 and are abruptly thickened in or near the middle to a central tyle 12-15 m in 

 diameter. Several short truncate cylindrical spines, as much as 9 ju long and 4 n 

 thick, arise from this tyle. Low and broad truncate protuberances also occur 

 on other parts of the shaft. The terminal anchors are 113-140 ^ long, usually 

 a little over a third of the whole spicule, and 97-102 n broad. The proportion 

 of their length to their breadth is 100 to 73-87, on an average 100 : 77.3. The 

 anchor-teeth are usually arranged in the ordinary, strictly verticillate manner, 

 but occasionally an amphidisc of this kind is met in which one of the teeth arises 

 at a much lower level than the rest (Plate 65, fig. 1). The anchor-teeth arise 

 nearly vertically from the shaft. They are curved more strongly in their basal 

 part and less strongly in their distal part than the anchor-teeth of the large 

 macramphidiscs with apically broad anchors described above. Their total curva- 

 tm'e is such that their ends usually diverge slightly from the shaft. Sometimes, 

 however, their tips are parallel or even sUghtly convergent. The ends of the 

 teeth are usually pointed. 



In form A these spicules (Plate 66, figs. 1, 2, 5) are similar, but on the whole 

 smaller. They are here 245-330 ^ long; the shaft is 7-10 n thick, and the central 

 tyle 13-16 fi. Cylindrical truncate spines 4 ij. long and 3-4 /x thick arise from 

 the latter. The remainder of the shaft usually bears a good many low and broad 

 protuberances. The anchors are 95-130 /j. long and 80-105 ^ broad. The 

 proportion of their length to their breadth is 100 to 79-88, on an average 

 100:83.6. 



