260 HYALONEMA (PRIONEMA) AGUJANUM. 



It is different with the amphidiscs with smooth teeth, stouter shaft, and 

 broader anchors. There is a great gap in the length frequency-curve of these 

 spicules in all the three forms: — in the var. tenuis, form A, curve between 80 and 

 225 ix] in the var. tenuis, form B, curve between 78 and 200 m; and in the var. 

 lata curve between 64 and 207 m- This clearly divides these spicules biometri- 

 cally into two groups: — macramphidiscs over 200, and micramphidiscs under 

 80 M in length. 



Besides one well-pronounced main elevation each of the three length fre- 

 quency-curves of the macramphidiscs shows only a quite insignificant secondary 

 elevation. The macramphidisc group can therefore be considered as fairly 

 homogeneous. 



The micramphidiscs on the other hand show clearly pronounced gaps in the 

 length frequency-curves; in the var. tenuis, irom A, curve between 30 and 51 ju; 

 in the var. tenuis, form B, curve between 33 and 47 //; and in the var. lata curve 

 between 26.8 and 47 m- These gaps divide them into two distinct groups, one 

 comprising the micramphidiscs over 47 yu in length, the other the micramphidiscs 

 under 33 m in length. For this reason, and because the former are also distin- 

 guished from the latter by their shafts, which in the larger ones are provided 

 with a relatively very large central tyle, and which in the smaller ones are not 

 thickened at all, or only slightly so at or near the centre, I divide the micram- 

 phidiscs into two secondary groups: — large micramphidiscs with well-developed 

 central tyle, and small micramphidiscs with no central thickening or only a 

 slight one. 



Thus four kinds of amphidiscs are to be distinguished : — macramphidiscs, 

 serrated amphidiscs, large micramphidiscs, and small micramphidiscs. 



The normal macrampliidiscs (Plate 73, figs. 1-7; Plate 75, figs. 3-21; Plate 

 77, figs. 1, 9, 10; Plate 78, figs. 12-15) have a straight and stout cylindrical shaft, 

 slightly thickened at or near the middle to a central tyle. A verticil of stout 

 and short, distally attenuated, truncate spines arises from this tyle. The 

 number of spines forming the verticil is variable but never great, most frequently 

 four to eight. The verticil is regular or irregular. Its irregularity is usually 

 slight, rarely considerable. In the latter case there are more than eight spines. 

 The remaining parts of the shaft are either quite smooth or they bear only a few 

 scattered spines nearly as broad as the spines of the central tyle, but usually 

 much shorter. 



The terminal anchors are composed of eight teeth quite uniformly curved 

 throughout (Plate 73, figs. 4, 6) or more strongly bent at the ends than elsewhere 

 (Plate 73, fig. 5). Their curvature is such that the end-parts of the teeth are 



