HYALONEMA (PRIONEMA) PINULIFUSUM. 291 



The large serrated mesatnphidiscs (Plate 72, figs. 1, 2) are 280-380 n long, 

 most frequently about 295 m- The shaft is straight, for the greater part of its 

 length cyhndrical, and 8-15 ix thick. It is gradually thickened towards the 

 ends, and abruptly thickened at or near the middle to a central tyle 14-22 fi 

 in transverse diameter, that is 5-7 ^ more than the adjacent parts of the shaft. 

 The central tyle bears a verticil of spines, which is either regular and situated 

 in a plane vertical to the axis of the shaft or irregular and oblique to the axis 

 of the shaft. The individual spines are 2-13 m long, and 2-6 yu thick at the base. 

 Their end-parts are generally more or less, sometimes very considerably, curved. 

 The remaining parts of the shaft bear a smaller or larger number of similar but 

 smaller and less curved spines. 



The terminal anchors are usually regular, more rarely irregular, with longer 

 teeth on one side than on the other. The tips of the teeth of such anchors he 

 in a plane oblique to the axis of the shaft. If one anchor is thus obhque, the 

 other anchor of the same spicule is generally oblique to the same extent, but in 

 the opposite direction, so that the two planes passing through the tips of the 

 teeth of the two anchors are approximately parallel. In a large serrated mes- 

 amphidisc in which this obliqueness of the anchors was particularly pronounced, 

 I found the spine-verticil on the central tyle oblique also, but in a direction 

 opposite to that of the two planes passing through the tips of the anchor-teeth. 

 The anchors are 111-155 ^ long, a little over two fifths of the whole spicule, 

 and 67-116 ii broad. The proportion of their length to their breadth is 100 to 

 56-75, on an average 100 : 66.5. The upper (outer) band-shaped parts of the 

 individual anchor-teeth are 15-23 fi broad in their middle-part. They taper 

 gradually to the rounded or abruptly pointed end. The teeth are curved down- 

 ward (inward) ; more strongly in their basal part, and often at a point lying near 

 the end; less strongly in their other parts. This curvature is, on the whole, 

 such that the ends of the teeth converge considerably. The ends of the anchors 

 are generally 9-17 fi narrower than their broadest parts, above. The lateral 

 margins of the teeth are distinctly serrated. The serration is quite regular in 

 the proximal and middle-parts of the teeth, but often irregular in their end-parts. 

 The saw-teeth are generally higher than broad, sharp-pointed, and close together. 

 They measure 1-3 m in length and 1-2 fi in breadth. 



The small serrated mesamphidiscs are similar to the large ones. Their 

 principal dimensions are: — total length 214-240 n, most frequently about 215 m; 

 length of anchors 83-110 ju; breadth of anchors 52-68 m; proportion of anchor- 

 length to anchor-breadth 100 to 59-66, on an average 100 : 62.3. 



