HYALONEMA (HYALONEMA) AGASSIZI. 181 



est length near the middle of the ray and from here decrease in size both proxi- 

 mally and distally. The largest spines are 10-21 n long and 2.5 fi thick at the 

 base. The maximum transverse diameter of the distal ray, together with the 

 spines, is 21-41 ju, usually 30-40 m, on an average 34.1 ti. The lateral rays 

 of the pentactine and hexactine gastral cone-pinules are, in the same spicule, 

 fairly equal (Plate 42, figs. 1, 10, 11) or more or less unequal (Plate 42, figs. 3, 5, 

 12), some of the lateral rays of the same spicule often being short, cylindrical, 

 and terminally rounded, the others long, conic, and pointed. The individual 

 lateral rays are 20-85 n long, straight, cylindrical, and terminally rounded, or 

 conic and pointed at the end. Their basal part is usually quite smooth, their 

 distal part for two thirds or more of their length is covered with more or less 

 conspicuous spines. The proximal ray in the hexactine forms is 17-76 n long, 

 gradually attenuated towards the end, or abruptly pointed. It is smooth 

 throughout, or covered with spines in its distal part. The proximal ray of the 

 diactine cone-pinule (Plate 42, fig. 13) is 95 n long. 



The gastral pinnies of the inner surface of the gastral wall of form A are 

 similar to those of the cone, but have distal rays only 91-112 /x long. 



The gastral cone-pinules of form B (Plate 42, figs. 14, 15) are pentactine or, 

 more rarely, hexactine and similar to those of form A. They have, however, 

 shorter distal rays with more divergent and longer spines. The distal ray is 

 in these spicules 83-109 ^ long, on an average 98.2 fi, and 5-7 fx thick at the base. 

 Its maximum transverse diameter, together with the spines, is 27-45 yu, on an 

 average 34.4 ix. Its largest spines attain a length of 25 m- The lateral rays are 

 30-48 fi long, the proximal ray (of the hexactine forms) is 12-27 n long. 



The gastral cone-pinules of form C (Plate 42, figs. 16, 17) have a longer 

 distal ray than those of form B and resemble those of form A very closely. 

 The distal ray in these spicules is 110-127 n long, on an average 118.5 m, and 

 4.5-5.5 M thick at the base. Its maximum transverse diameter, together with 

 the spines, is 24-29 /x. The lateral rays are 35-50 m long. 



The distal rays of the gastral pinules of the inner surface of the gastral wall 

 of form C (Plate 42, figs. 18, 19) are similar in size but have more divergent 

 spines and consequently, together with the spines, a greater maximum trans- 

 verse diameter. The divergence of the proximal spines from the tip of the ray 

 is so great that some of them stand vertical, and some even point the opposite 

 way. The distal ray is 103-126 m long, on an average 115 fx, and 5-6 /x thick at 

 the base. Its maximum transverse diameter, together with the spines, is 28-35 ^l. 

 The lateral rays are 36-50 ix long. 



