180 
HYALONEMA (HYALONEMA) AGASSIZI. 
of 350-640 fj.. The distal ray is 148-245 m long, fairly straight, 6-9 m thick at 
the base, and thickened above. It ends with a smooth, rather slender, sharp- 
pointed terminal cone. All parts of it, with the exception of its basal portion 
and its terminal cone, are covered with spines strongly inclined towards the tip. 
The largest spines are situated about a third of the length of the distal ray from 
the tip. From here they decrease in size both distally and proximally. The 
largest spines are 6-7 m long and 2-3 m thick at the base. The maximum trans- 
verse diameter of the distal ray, together with the spines, is 15-26 m- The lateral 
rays are generally reduced to mere rounded protuberances, only exceptionally as 
much as 9 m high (Plate 44 , fig. 2, the left one). Together they form a central 
tyle 11-21 /x in diameter. The proximal ray is straight or slightly curved, 
175-400 n long, and, at the base, as thick as the distal ray. It usually bears a 
few spines and a number of very low and broad rounded protuberances which 
render the appearance of its outline somewhat wavy. 
I have observed a few transitional forms which appear to connect these 
diactine pinnies with ordinary, centrotyle, amphiox megascleres. The ray corre- 
sponding to the distal ray of the diactine pinnies of one of these spicules, which 
I measured, was perfectly smooth, 680 \x long, and 22 /x thick at the base, and 
thickened above the middle of its length to 26 /x. Its central tyle measured 
30 ix in transverse diameter. 
The gastral pinules (Plate 42 , figs. 1-8, 10-19, 24). In form A, where 
the gastral pinules both on the cone and on the inner face of the gastral wall 
could be conveniently measured, I found the distal rays of the former markedly 
longer than the distal rays of the latter, and also noticed that the distal rays of 
the pinules of the gastral wall decreased in length towards the upper, free margin. 
The gastral pinules of the cone of form A (Plate 42 , figs. 1-8, 10-13) are for 
the most part pentactine; a few, however, are hexactine (Plate 42 , figs. 1, 2) 
and one that I observed was diactine (Plate 42 , fig. 13). The distal ray in these 
pinules, when normally developed, is 97-135 /x long, usually 100-134 /x , on an 
average 118.2 n, and 3. 5-9. 5 m thick at the base. One (Plate 42 , fig. 8) that 
had apparently been broken off during growth and then partly regenerated 
was only 65 /x long. The distal ray-ends with a smooth, blunt, terminal cone 
4.5-9 m thick. This and the basal part of the ray are destitute of spines. The 
remaining parts of it bear somewhat sparse spines. The proximal spines are 
strongly divergent, only slightly inclined, and curved towards the tip of the ray. 
Distally they become more inclined in this direction, but are, on the whole, much 
more divergent than those of the dermal pinules. The spines attain their great- 
