HYALONEMA (HYALONEMA) TYLOSTYLUM. 233 



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

 shorter and nearly straight spines, which are 3-6 ^ long, exceptionally 12 m, and 

 3-5.5 M thick. 



The terminal anchors are 95-148 m long, usually a little over a third of the 

 whole spicule, and 60-114 fi broad. The proportion of their length to their 

 breadth is 100 to 57-89, on an average 100 : 73.7. .Although both in the larger 

 and the smaller of these spicules relatively broad and relatively slender anchors 

 are met, yet the relative anchor-breadth is, on the whole, correlated to the 

 length of the spicule, so that, roughly speaking, the smaller the amphidisc the 

 more slender the anchors. In the largest large macramphidiscs, over 350 ix 

 in length, the proportion of anchor-length to anchor-breadth is 100 to 62-89, 

 on an average 100 : 78; in the smaller large macramphidiscs, under 350 m in 

 length, this proportion is 100 to 57-79, on an average 100 : 68.6. 



The anchor consists of eight teeth. The individual teeth arise vertically 

 from the shaft, are considerably curved, concave to the shaft in their proximal 

 part, and slightly and quite uniformly curved in the same direction in their 

 distal and middle-parts. The curvature is such that the end-parts of the teeth 

 az'e parallel or sUghtly convergent. In the latter case the end of the anchor is 

 of course narrower than a portion of its middle-part. The anchor-breadth 

 measurements given above are always the maximum breadths. The anchor- 

 end breadth may be 14 yu less than the maximum breadth. The teeth have the 

 usual T-shaped transverse section. The upper and outer part, which corre- 

 sponds to the upper stroke of the T, is a thin band of a fairly uniform breadth of 

 13-18 y., to within a short distance of the end. The end itself is abruptly and 

 not sharply pointed. The lower and inner keel, which corresponds to the lower 

 stroke of the T, is 13-16 ix high near the base of the tooth and becomes gradually 

 narrower towards the tip. 



The small macramphidiscs (Plate 69, figs. 20-23) are similar to the large 

 ones, but have relatively narrower anchors, less distinct central tyles, and more 

 spines on the shaft. These spicules are 116-240 ^ long, most frequently 130- 

 220 fi. The shaft is 2.2-6 ^ thick. The central tyle is 4-14 m in transverse 

 diameter, that is 1.8-9 m more than the adjacent parts of the shaft. It bears a 

 verticil of nearly straight, or, more rarely, strongly curved spines, which are 

 vertical or obhque to the axis of the shaft. These spines are generally cyhndro- 

 conical, blunt, and 3-5 n long. The remaining parts of the shaft are covered 

 with much smaller spines. These are the more numerous and the more slender 

 the smaller the spicule. 



