268 HYALONEMA (PRIONEMA) AZUERONE. 



of these spicules are: — distal ray, length 134-290 /z, basal thickness 4-5 a^, 

 maximum tliickness together with the spines 13-28 ^i lateral rays, length 26- 

 52 IX ; proximal ray (when present) , length 35-38 m- 



The hexactine megascleres measured were 0.7-2.4 mm. in diameter, and had 

 smooth, conic, blunt-pointed rays, 17-45 ^ thick at the base. 



The pentactine megascleres measured had straight rays, 10-25 ^ thick at 

 the base. The proximal ray is 0.1-0.(3 mm. long; the lateral rays, which enclose 

 angles of about 80° with the proximal, are 150-300 n long. 



The fairly isoactine 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 ^ thick in 

 their middle-part. The central tyle is 12-28 m 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 anisoactine centrotyle rhabds are 1-2.5 mm. long, usually 

 slightly curved, and 13-15 n thick near the morphological centre. Their central 

 tyle measures 14-16 ^ in diameter. The terminal thickening (tyle) of the 

 reduced ray is 17-20 ^ 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 n in diameter were observed. 



The microhexactines (Plate 57, figs. 18-23; Plate 58, fig. Ic) measure 

 50-160 M in diameter, usually 70-110 /i. The rays of the same spicule are gen- 

 erally equal. They are smooth, at the base 1-3.5 m thick, usually about 1.8 /x, 

 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 /u 

 in diameter, having nearly straight rays. One of the microhexactines observed 

 had a bifurcate ray (Plate 57, fig. 20). 



The rare micropentactines measured were 94-150 yu in diameter, and had 

 rays 1.5-3 fi thick at the base. 



One of the rare diactine microhexactine-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 /i long, the other bifurcate and 50 m 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 



