298 HYALONEMA (PRIONEMA) FIMBRIATUM. 
with the true pinules. The slender-rayed long-spined basals may therefore be 
considered as pinule-derivates. 
The acanthophores with stout rays are monactine to pentactine. 
Among the tri- to pentactine acanthophores (Plate 63, figs. 15-19) the tetrac- 
tines with four rays extending in one plane (stauractines) greatly predominate. 
The maximum diameter of these spicules usually is 330-670 », but much smaller 
forms only 100-300 » in diameter (Plate 63, fig. 15) also occur. The rays are 
equal or unequal, fairly straight, 10-28 u thick at the base, and slightly attenu- 
ated distally. They often have a somewhat wavy outline. Their end-parts 
are usually thickened, densely covered with rather short, broad spines, and 
blunt-pointed, or, particularly in the cases where the rays are reduced in length, 
terminally rounded. The thickened, spiny end-parts of properly developed 
long rays are accordingly usually spindle-shaped, those of reduced, short rays 
usually more or less spherical. 
Of the diactine or monactine forms, that is the rhabd acanthophores, various 
kinds can be distinguished: — slender, long-spined tylostyles; angularly bent 
centrotyle diactines; straight or slightly curved, stout, centrotyle diactines; 
stout, strongly curved, not centrotyle rhabds with thickened ends; slender, 
slightly curved, long rhabds with thickened ends; and strongly curved rhabds 
of the last mentioned sort. 
The slender tylostyle monactine acanthophores with long spines are very rare. 
A spicule of this kind measured was 220 u long and 8 » thick; its terminal tyle 
measured 18 » in diameter. I am inclined to consider these spicules as monac- 
tine-derivates of the slender-rayed long-spined basal tri- to hexactines above 
described. 
The angularly bent centrotyle diactine acanthophores are also very rare. They 
have a spiny tyle and two straight rays enclosing an angle of about 90°. In one 
of these spicules measured, the two actines were quite straight, and respectively 
13 » thick and 430 and 500 » long. The spiny central tyle was 28 u in diameter. 
The stout, straight or slightly curved, centrotyle diactine acanthophores (Plate 
63, figs. 20-23) are usually 550-920 u long, and 14-30 » thick near the centre. 
The central tyle is 20-54 » in diameter. The proportion of the thickness of the 
tyle to the thickness of the adjacent parts of the spicule is 114-300 : 100. When 
the tyle is large, it is spiny (Plate 63, fig. 20); when it is small, it is smooth 
(Plate 63, figs. 21-23). The two rays of these spicules have the same shape as 
the rays of the tri- to pentactine stout-rayed basals above described, but are 
on the whole longer. I think there can be no doubt about these spicules being 
diactine-derivates of the stout-rayed tri- to pentactine acanthophores. 
