168 
HYALONEMA (HYALONEMA) OBTUSUM. 
Length of Amphidiscs (/A 
Fig. 4.- — ■ Length frequency-curve. 
between its distances from the two ends is 7-37 n, 3%-15% of the length of the 
whole spicule. In the shaft an axial thread is distinctly visible (Plate 37, fig. 21). 
This thread appears to be quite simple and it certainly does not give off branches 
in the central tyle. From the central tyle, and also from other parts of the shaft, 
spines arise. The spines of the central tyle are generally five to eight in number 
and arranged in a more or less regular verticil. They are conical, blunt-pointed, 
or truncate, 9-14 n long, exceptionally 18 n, and 5-7 n thick at the base; the 
truncate ones bear minute secondary spinelets on their ends. The other spines 
are irregularly scattered over the middle-part of the shaft. The thickened 
conical end-parts of the shaft are free from spines. These spines are not very 
numerous; often there are a good many more spines on one side of the central 
tyle than on the other. Most of these spines are vertical to the axis of the shaft; 
a few of them are, however, oblique, inclined toward the centre of the spicule. 
These scattered spines are similar in shape and about as stout, but, as a rule, 
are shorter than the spines of the central tyle. The spines are destitute of 
axial threads. 
