HYALONEMA (PHIALONEMA) BREVANCORA. 361 



gradually thickened to about double its minimum thickness near the middle. 

 The central thickening bears a verticil of conic, truncate spines, 5-10 m long, 

 and 3-4 ^ thick at the base. The truncate ends of these spines bear clusters 

 of very minute, short, secondary spinelets. One of the large macramphidiscs 

 observed was destitute alike of the central tyle and the central spine-verticil. 

 Apart from this spine-vei'ticil, the shaft is, in all the large macramphidiscs 

 observed, entirely smooth. The terminal anchors are 25—41 n long, about a 

 tenth of the whole spicule, and 5.3-72 /i broad. The proportion of the length 

 to the breadth of these anchors is 100 : 145 to 100 : 240, on an average 100 : 203. 

 The anchor usually consists of eight teeth. The individual teeth are either 

 uniformly curved, concave to the shaft throughout, or thus curved only in their 

 basal and middle-part, and abruptly bent down at the end. The end-parts of 

 the teeth enclose angles of about 25° with the axis of the shaft. The basal parts 

 of the teeth appear to be massive ; distally they thin out to rounded, spoon-like 

 lamellae about 15 m broad. 



The micramphidiscs range from 18 to 38 /x in length. In the frequency- 

 curve pertaining to this dimension there is a marked depression at about 33 jit. 

 The micramphidiscs shorter than this have, as a rule, nearly smooth shafts; 

 those as large or larger than this, very spiny shafts. I consider the former as 

 small, the latter as large micramphidiscs. 



The large micramphidiscs (Plate 55, figs. 10-12) are 33-38 /i long, most 

 frequently about 36 yu. The shaft is cylindrical, 1.6-1.8 m thick, and covered 

 with numerous irregularly scattered spines. The terminal anchors are 7-11 n 

 long, a sixth to a fourth of the whole spicule, and 8-10.5 ^ broad. The propor- 

 tion of anchor-length to anchor-breadth is 100 : 90 to 100 : 114, on an average 

 100 : 104. The individual teeth are rather strongly and uniformly curved in 

 their basal part; distally the radius of curvature increases. Their nearly 

 straight end-parts are approximately parallel to the shaft. 



The small micramphidiscs (Plate 55, figs. 7-9, 13) are 18-32 yu long, most 

 frequently about 26 m- The shaft is straight, cylindrical, and 1.2-1.6 fi thick. 

 It is smooth, or bears a few small spines in its middle-part. The anchors are 4-8 fi 

 long, a sixth to nearly a third of the whole spicule, and 7-9.5 ii broad. The 

 proportion of anchor-length to anchor-breadth is 100 : 100 to 100 : 180, on an 

 average 100 : 131. The anchor-teeth of the small micramphidiscs are, in respect 

 to their curvature, similar to those of the large micramphidiscs above described. 



Although the fragmentary condition of the specimens renders it difficult 

 to decide to which genus of Amphidiscophora they belong, the probability is 



