HYALONEMA (PRIONEMA) AZUERONE. 269 



small regular anchors; and D small amphidiscs with stout shafts and relativelj' 

 large, usually more or less irregular anchors. Biometrically, according to 

 the length frequency, A is a well-defined, simple, and homogeneous group. 

 B overlaps C and D somewhat, and C and D are about equal in length. B 

 is biometrically composed of three secondary groups represented by (a), large, 

 (6), medium sized, and ic), small amphidiscs. C is biometrically a simple 

 and homogeneous group. D is biometrically composed of two well-defined 

 secondary groups represented by larger amphidiscs (a), and smaller amphi- 

 discs (6). Thus if both their shape and the biometric character of their length- 

 frequencies are taken into consideration seven kinds of amphidiscs are to 

 be distinguished : — macramphidiscs (^4 ) ; large mesamphidiscs {B a) ; medium 

 mesamphidiscs (5 h) ; small mesamphidiscs {B c) ; slender-shafted micram- 

 phidiscs (C) ; stout-shafted large micramphidiscs {D a) ; and stout-shafted small 

 micramphidiscs {D b) . 



The macramphidiscs (Plate 57, figs. 1-5; Plate 58, figs. 5-9) are 300-356 ^ 

 long, most frequently about 320 fi. Their shaft, which is straight and for the 

 most part 7-9 ij. thick, thickens at the ends gradually to a conic extension 10-14 /x 

 in diameter, and in or near the middle abruptly to a central tyle of the same 

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

 to the thickness of the central tyle is 100 to 130-200, on an average 100 : 157.4. 

 An irregular verticil of cylindroconic, truncate, or terminally rounded spines arises 

 from the central tyle. These spines are 1.5-3.5 ^ thick, usually 1.5-4 ^ long, 

 sometimes as much as 8 ;u, and when long are irregularly curved. They bear 

 on their terminal face a cluster of exceedingly minute secondary spinelets. 

 Scattered spines, similar to those of the central tyle, but on the whole shorter, 

 are met on the remaining parts of the shaft. The terminal anchors are 77- 

 119 M long; they are broadest usually a little over a third of the whole spicule, 

 somewhere beyond the middle, and attenuated towards the end. Their maxi- 

 mum breadth is 85-104 n, their end-breadth 75-95 n. The proportion of length 

 to maximum breadth is 100 to 77-114, on an average 100 : 101.5. The maxi- 

 mum breadth is 3-11 n, on an average 7.1 m, greater than the end-breadth. The 

 anchor usually consists of nine or ten teeth. The individual teeth arise steeply 

 from the end of the shaft, and are strongly curved in their basal part. Farther 

 on the curvature decreases either gradually or somewhat abruptly. The 

 decrease of curvature either continues to the end of the tooth, or it increases 

 again just before the end. The total curvature is such that the end-parts of 

 the teeth converge toward the shaft, with the axis of which they usually enclose 



