HYALONEMA (HYALONEMA) GRAND ANGORA. 
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rically by a distinct gap in the length frequency-curve. The large macramphi- 
discs form, as the graph shows, a biometrically perfectly homogeneous group. 
Also among the micramphidiscs two morphologically and biometrically 
distinct kinds can be distinguished: — a larger kind, over 37 n in length, with 
longer anchors and stout central tyle ; and a smaller kind, under 31 n in length, 
with shorter anchors and a relatively much smaller central tyle, or no central 
tyle at all. The part of the length frequency-curve pertaining to the first, 
larger kind of micramphidiscs shows several ups and downs, so that this group 
cannot be considered biometrically homogeneous. However, in view of the 
morphological similarity of these larger micramphidiscs of various size, I do not 
think the depressions in this part of the curve (none of which extends down to 
the base (0) line) sufficient for a division of them into secondary groups. The 
second, smaller kind of micramphidiscs forms a biometrically homogeneous 
group. 
I distinguish accordingly four kinds of amphidiscs in this sponge: — large 
macramphidiscs, small macramphidiscs, large micramphidiscs, and small micr- 
amphidiscs. 
The large macramphidiscs (Plate 78 , figs. 16-19; Plate 79 , figs. 1, 2, 26) 
are 318-510 /x long, most frequently about 415 m- The shaft is generally straight, 
very rarely bent, cylindrical, 20-26 /x thick, and thickened gradually towards 
the ends, and abruptly in or near the middle to a central tyle 24-30 /x in trans- 
verse diameter, that is 3-7 ^ more than the adjacent parts of the shaft. The 
central tyle bears a verticil of truncate conical spines. These spines are usually 
fairly equal, 10-20 m long and 10-12 m thick at the base. Sometimes one or two 
are large and the others more or less rudimentary. The remaining parts of the 
shaft are either quite smooth (Plate 79 , fig. 2), or they bear only one or very 
few protuberances, about as broad as the spines of the central tyle, but 
generally much shorter. 
The terminal anchors are 83-125 /x long, a quarter to a sixth of the whole 
spicule, and 135-200 ^ broad. The proportion of anchor-length to anchor- 
breadth is 100 to 142-190, on an average 100 : 165.4. The anchor consists of 
eight teeth. The individual teeth arise vertically from the end of the shaft, 
and are curved more strongly in their proximal than in their distal half. The 
extreme tips of the teeth are sometimes slightly and abruptly bent inwards. 
The curvature of the teeth is, on the whole, such that their end-parts generally 
diverge slightly from the axis of the shaft. 
The dimensions of the single small macramphidisc observed are: — length 
