HYALONEMA (PRIONEMA) SPIXOSUM. 277 



teeth. One of the abnormal forms is represented on Plate 49, fig. 10. This 

 spicule is 235 ^ long, its shaft is 5 ^ thick, central tyle 9 ^ thick. A verticil of 

 short, laterally compressed, distally broadened and truncate, band-shaped 

 spines arises from the tyle. The remainder of the shaft bears short, truncate, 

 cylindrical spines. The anchors are about 54 ^ long, 33 m broad. The anchor- 

 teeth have serrated margins, are strongly curved in their basal part, but nearly 

 straight in their middle- and end-parts. The latter are nearly parallel to the 

 shaft. Another similar spicule observed was only 180 ju long. I have also seen a 

 few large macramphidiscs in which the spines on the central tyle were similar 

 to the teeth of the terminal anchors, and all curved in one direction, so that the 

 verticil formed by them was like a terminal anchor, only smaller. 



The rare small macramphidiscs (Plate 49, figs. 5, 6) differ from the large 

 macramphidiscs — apart from their smaller size — chiefly by being destitute 

 of long central spines. The small macramphidiscs are 45-126 ju long. The shaft 

 is 1-3 II thick, and either simply cylindrical (Plate 49, fig. 5) or gradually thick- 

 ened at or near the middle (Plate 49, fig. 6) to a tyle sometimes 5.5 ix in transverse 

 diameter. The proportion of the thickness of the adjacent parts of the shaft to 

 the diameter of the tj'le is 1 : 1 (when there is no tyle) ; 1 : 2.2 (when the 

 tyle is most highly developed) . The whole of the shaft is uniformly and densely 

 covered with small spines. The spines on the tyle are not larger than the 

 others. The anchors are 13-56 ix long, a third or less of the whole spicule, and 

 12-43 11 broad. The proportion of the length to the breadth of the anchors 

 is 100 to 77-92, on an average 100 : SO. The individual teeth appear to differ 

 from those of the large macramphidiscs only by being smaller. 



The large micramphidiscs are \er3- rare. In fact only two could be measured. 

 These are 51 and 56 m long, and have anchors 16 and 19 m long and 8.5 and 9 ^ 

 broad respectivelj'. The proportion of length to breadth of their anchors is 

 100 : 56 and 100 : 44. 



The sTtiall micramphidiscs (Plate 48, figs. 28-31; Plate 49, figs. 1-4) are, 

 although much more abundant than the other amphidisc-forms, still not nearly 

 so frequent as in other hyalonematids. They are 13-29 n long, usually 17-27 ju, 

 and have a shaft 0.8-1.7 ii thick. The shaft generally bears a larger or a smaller 

 number of minute, cylindrical, truncate, vertical or oblique spines. These 

 spines are irregularly distributed; often they form a little cluster near the centre 

 of the shaft. The anchors are 4-7.5 m long, a fifth to a third of the whole spicule, 

 and 5-8 n broad. The proportion of their length to their breadth is 100 to 87- 

 175, on an average 100 : 134.8. The individual anchor-teeth are strongly curved 



