268 
HYALONEMA (PRIONEMA) AZUERONE. 
of these spicules are: — -distal ray, length 134-290 n, basal thickness 4-5 n, 
maximum thickness together with the spines 13-28 ix; lateral rays, length 26- 
52 ix ; proximal ray (when present) , length 35-38 /x. 
The hexadine megasderes measured were 0.7-2. 4 mm. in diameter, and had 
smooth, conic, blunt-pointed rays, 17-45 m thick at the base. 
The pentadine megasderes measured had straight rays, 10-25 fx thick at 
the base. The proximal ray is 0. 1-0.6 mm. long; the lateral rays, which enclose 
angles of about 80° with the proximal, are 150-300 n long. 
The fairly isoadine centrotyle amphiox rhabds are more or less, often very 
considerably curved, particularly the long ones. They are usually blunt-pointed, 
near the end sometimes wavy in outline, 0.6-2. 8 mm. long, and 9-25 m thick in 
their middle-part. The central tyle is 12-28 n in transverse diameter, the 
proportion between the thickness of the adjacent parts of the spicule and the 
thickness of the tyle being 100 to 108-151, on an average 100 : 120.6. 
The tylostyle-like anisoadine centrotyle rhabds are 1-2.5 mm. long, usually 
slightly curved, and 13-15 /x thick near the morphological centre. Their central 
tyle measures 14-16 ix in diameter. The terminal thickening (tyle) of the 
reduced ray is 17-20 n in diameter. Besides the intact tylostyle-like spicules, 
the measurements of which are given above, some fragments of them with a 
terminal tyle sometimes 23 fx in diameter were observed. 
The microhexadines (Plate 57 , figs. 18-23; Plate 58 , fig. lc) measure 
50-160 n in diameter, usually 70-110 /x. The rays of the same spicule are gen- 
erally equal. They are smooth, at the base 1-3.5 ix thick, usually about 1.8 n, 
straight in their proximal part and generally slightly curved in their distal part. 
Their curvature appears to be, on the whole, in inverse proportion to the size 
of the spicule; the largest microhexactines, that is those more than 125 fx 
in diameter, having nearly straight rays. One of the microhexactines observed 
had a bifurcate ray (Plate 57 , fig. 20). 
The rare micropentadines measured were 94-150 ix in diameter, and had 
rays 1.5-3 m thick at the base. 
One of the rare diadine microhexadine-derivates measured consisted of two 
straight rays forming an angle of 85°. Its rays are 3 n thick at the base; one 
is simple and 60 m long, the other bifurcate and 50 ix long. 
The amphidiscs. According to their shape, four kinds of amphidiscs are to 
be distinguished : — A large amphidiscs with relatively short anchors and 
serrated anchor-teeth; B medium amphidiscs with relatively long anchors and 
smooth anchor-teeth; C small amphidiscs with slender shafts and relatively 
