158 HYALONEMA (HYALONEMA) OBTUSUM. 



maximum transverse diameter of the distal ray, together with the spines is 

 18-32 IX. The distal ray of the dermal pinules of var. rohisia is 140-172 ^ 

 long and 5-8 n thick at the base. The maximum transverse diameter of this ray, 

 together with its spines, is 25-40 /x. 



The proximal apical ray, of the hexactine forms of var. gracilis, (Plate 35, 

 figs. 29, 30) is straight, 10-42 n long, and 3.7-4.5 m thick at the base. It is 

 cylindroconic, generally abruptly and sharply pointed, and covered with minute 

 spines. 



The four lateral rays of the same spicule are usually fairly equal, the greatest 

 difference of length observed not exceeding 4 /i. The lateral rays are straight; 

 in the dermal spinules of var. gracilis they are 20-40 /j. long, rarely up to 50 n, 

 and 3-5 n thick at the base; in those of var. robusta they are sometimes (Plate 40, 

 fig. 4) much shorter, 10-36 m long. They are cj'lindroconic, rounded or, more 

 rarely, abruptly pointed, and covered with minute spines. 



The gastral pinules (Plate 35, figs, la, 2, 3a, 4-9, 16; Plate 40, fig. 3) are, like 

 the dermal pinules, mostly pentactine; hexactine forms, however, also occur dif- 

 fering from the pentactine only by possessing a sixth apical proximal ray. The 

 distal ray is straight; in the gastral pinules of var. gracilis, it is 73-145 m long, 

 usually 77-135 m, and 4.5-5.5 /x thick at the base, in the gastral pinules of var. 

 robusta 94-140 m long and 5-7 n thick at the base. It is thickened above, and 

 attains its greatest thickness a little way beyond the middle of its length ; then 

 it again becomes thinner, and it ends in a usually sharp-pointed, rather slender, 

 terminal cone, which does not exceed the proximal end of the ray in thickness. 

 The proximal end-part and the distal cone of the ray are smooth; its middle-part 

 bears spines. The spines on the proximal half of the distal ray are very sparse, 

 point obliquely upward, and are strongly divergent, the angles enclosed between 

 them and the ray being 40°-55°. The spines on the distal half of the ray are 

 smaller, more crowded, and less divergent, their size decreasing and their inclina- 

 tion increasing towards the end of the ray. They attain a length of 15-25 m 

 and a basal thickness of 3-4.5 m- The maximum transverse diameter of the 

 distal ray, together with the spines, is in both varieties 26-45 n. 



The proximal ray (of the hexactine forms) (Plate 35, fig. 4; Plate 40, fig. 3) 

 is straight, 43-74 n long, 4.5-5.5 m thick at the base, conical, pointed, and spiny. 



The four lateral rays of the same spicule are fairly equal or rather unequal 

 in size; the maximum difference observed in their length was 15 m- The lateral 

 rays are straight or, more rarely, sUghtly curved. Their length is subject to 

 considerable variation. They are in the gastral pinules of var. gracilis 35-90 ju 



