380 
HYALONEMA (SKIANEMA) AEQUATORIALE. 
such that the directions (tangents) of the proximal and distal end-parts of the 
ray generally enclose an angle of 105°-130°. The tips of opposite rays point in 
opposite directions. 
From a morphological point of view four kinds of amphidiscs are to be dis- 
tinguished: — A, larger forms with low (short) and very broad anchors, about a 
third of the length of the whole spicule; B, forms intermediate in size with rela- 
tively large anchors, about half as long as the whole spicule; C, forms inter- 
mediate in size with small, relatively broad anchors, a fourth to a fifth of the 
whole spicule in length ; and D, small forms with more slender anchors. 
As the length frequency-curves in Figure 24 show, these four morpho- 
logically different kinds of amphidiscs are by no means all clearly separated 
also biometrically. In fact the curve pertaining to the amphidiscs of the 
groups B and C overlap to a large extent, and only the curve pertaining to 
group D is clearly distinct from the others. 
In view of the great morphological difference between the groups B and C 
and the total absence of intermediate forms connecting these two groups, I 
do not hesitate to consider them as different kinds of amphidiscs. I distinguish 
altogether four different kinds of amphidiscs in this sponge: — large (group A) 
and small (group B) macramphidiscs, and large (group C ) and small (group D) 
micramphidiscs. The length frequency-curves pertaining to the first three forms 
are quite simple and without deep depressions; these groups are biometrically 
homogeneous. The curve pertaining to the small micramphidiscs (group D) 
is complicated, however, by two deep depressions descending to the 0-line, which 
divide it into three parts. Since, however, the larger, the medium, and the 
smaller small micramphidiscs pertaining to the three distinct elevations of this 
curve are quite similar in shape, I do not think it advisable to distinguish sub- 
groups within this amphidisc-group. 
The regular large viacr amphidiscs (Plate 99 , figs. 1 , 2, 37; Plate 100 , figs. 
5-11; Plate 101, fig. 2d) are 105-298 m long, usually 122-257 ^, most fre- 
quently about 180 /x. The shaft is straight, cylindrical, perfectly smooth, and 
14-27 m thick, generally 19-27 The terminal anchors are 42-87 /x long, 
about a third of the whole spicule, and 90-195 /j. broad. The proportion of the 
length to the breadth of the anchors is 100 to 191-288, on an average 100 : 
236.8. Each anchor consists of from eight to eleven teeth. The teeth of the 
two anchors of the same spicule are generally situated alternately. The teeth 
arise nearly vertically from the ends of the shaft, are curved very slightly in 
their proximal part, but very strongly in their distal part, and their tips converge 
