230 
HYALONEMA (HYALONEMA) TYLOSTYLUM. 
indicate that these sponges were, in life, cup-shaped and that they have lost 
their upper marginal part and have been compressed to lamellar structures 
without open gastral cavities during or after capture. 
The colour in spirit is dull brown. 
The skeleto7i. The distal rays of the dermal pinules form a dense fur on the 
intact parts of the outer surface (Plate 70 , figs. 3b, 8). Numerous amphidiscs, 
chiefly small macramphidiscs, occur in and just below the dermal membrane. 
The shafts of these spicules are situated radially. About one half of each of these 
amphidiscs with one anchor protrudes freely beyond the surface; the other 
half with the other anchor is imbedded in the sponge (Plate 70 , fig. 3a). The 
lateral rays of hypodermal pentactines extend just below the layer occupied by 
the lateral rays of the pinules. Large macramphidiscs with the shaft parallel or 
oblique to the surface occur a little farther. Besides these and down the proxi- 
mal rays of the hypodermal pentactines, small hexactine megascleres also occur 
in this region. The skeleton of the inner gastral face of the lamellae (cup-wall) 
consists of gastral pinules and hypogastral pentactines. Tylostyles, hexactines, 
numerous microhexactines, a few micropentactines, and a good many amphi- 
discs, chiefly small macramphidiscs and micramphidiscs, are met with in the 
choanosome amphioxes. 
The dermal pinules (Plate 70 , figs. 1, 2, 3b, 8) are pentactine and have a 
straight distal ray. One of the many observed was hexactine, and one other 
had an angularly bent distal ray. The distal ray is 340-379 n long, most fre- 
quently 342-368 ix, on an average 355 /x, and, at the base, 8-11 n thick, generally 
about 9 ix- Its basal end-part, for a distance of about 30 m, is smooth, thence 
onward the distal ray is spiny. The lowest spines are scarce, short, and very 
divergent. Distally, up to a point 100-120 ^ from the tip of the ray, the spines 
become more crowded, longer and more strongly inclined towards the ray. 
Farther on they again decrease in length and divergence, the uppermost being 
nearly parallel to the shaft. At the point of maximum thickness, which lies high 
up, the distal ray, together with the spines, is 31-47 ix in transverse diameter. 
The lateral rays are cylindrical, usually rounded at the end, spined, and 27-42 /x 
long, on an average 35 n. The single proximal ray observed was about as long 
as the laterals. 
All the gastral pinules (Plate 70 , figs. 9, 10) observed were pentactine. 
Their distal ray is straight, 120-245 /x long, most frequently 150-190 /x, on an 
average 166 /x, and, at the base, 5-10 m thick, generally about 8 m- It is sharp- 
pointed and markedly thickened some distance below the middle of its length. 
