322 
HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 
18-90 n long. It is to be noted that the macramphidiscs are much more numer- 
ous in a than in 6, while the micramphidiscs are much more numerous in b than 
in a. In consequence of this the number of macr- and micramphidiscs measured 
and plotted in the figure are very different in the two specimens, and the sum- 
mits of the two main elevations of the a- and 6-curve are very different in height. 
The larger (longer) macramphidiscs differ from the smaller (shorter) ones 
morphologically by having relatively shorter anchors. The length frequency- 
curves of the macramphidiscs show that these spicules by no means represent 
a biometrically homogeneous group in respect to their length. The parts of 
the macramphidisc curves below (to the left of) the above mentioned gaps 
between 200 and 220 p in a and between 187 and 212 p in 6 are very regular 
and obviously pertain to biometrically homogeneous groups; the parts of these 
curves above (to the right of) the gaps are on the other hand very irregular 1 
and in no way in harmony with the others below (to the left) of them. I there- 
fore think that the group macramphidiscs should be subdivided into two 
secondary groups : — large macramphidiscs with relatively short anchors, in 
both specimens together 212-492 p long; and small macramphidiscs with 
relatively long anchors, in both specimens together 110-200 p long. 
The length frequency-curves of the micramphidiscs of both specimens 
exhibit, besides the single main elevation, a number of small elevations. Most 
of these are, as in the case of the large macramphidiscs, probably due to the 
scarcity of the micramphidiscs of these sizes, which made it impossible to meas- 
ure a larger number of them. Some of these elevations (two in the a-curve; 
and one in the 6-curve, corresponding to one of the former) pertaining to the 
largest micramphidiscs are, however, separated from the rest of the micramphi- 
disc curves by very conspicuous gaps (between 54 and 79 p in the a- and between 
66 and 79 p in the 6-curve). I therefore think it well to divide the micramphi- 
discs according to these gaps into two subgroups: — large micramphidiscs, in 
both specimens together 79-90 p long; and small micramphidiscs, in both speci- 
mens together 18-66 p long. 
The chief dimensions of the large macramphidiscs (Plate 85 , figs. 1-7) are 
tabulated on page 323. 
In these amphidiscs the shaft is straight and usually centrotyle. It is 
either quite smooth (Plate 85 , fig. 7) or bears a few low rounded knobs (Plate 
85 , figs. 2, 4-6), sometimes also a single, straight, cylindrical, terminally rounded 
spine (Plate 85 , fig. 1 ), which arises from its centre (central tyle). Occasionally 
1 These irregularities are partly at least probably due to the rarity of these spicules, which made it 
impossible to measure a larger number of them. 
