180 HYALONEMA (HYALONEMA) AGASSIZI. 



of 350-640 IX. 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 n long and 2-3 yu thick at the base. The maximum trans- 

 verse diameter of the distal ray, together with the spines, is 15-26 n. 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 fx in diameter. The proximal ray is straight or slightly curved, 

 175-400 M long, and, at the base, as thick as the chstal 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 pinules with ordinary, centrotyle, amphiox megascleres. The ray corre- 

 sponding to the distal ray of the diactine pinules of one of these spicules, which 

 I measured, was perfectly smooth, 680 n long, and 22 n thick at the base, and 

 thickened above the middle of its length to 26 fi. Its central tyle measured 

 30 ;u in transverse diameter. 



The gastral pimdes (Plate 42, figs. 1-8, 10-19, 24). In form A, where 

 the gastral pinules lioth 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 n long, usually 100-134 n, on an 

 average 118.2 fx, 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 n long. The distal ray-ends with a smooth, l)lunt, terminal cone 

 4. .5-9 IX 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 sUghtly 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- 



