178 HYALONEMA (HYALONEMA) AGASSIZI. 



spines, which surround the terminal cone, are nearly parallel to the ray-axis. 

 The lowest spines are straight and quite short. Distally they become slightly 

 curved, concave towards the tip of the ray. Up to the middle of the length of 

 the ray they increase in size; beyond they again become smaller. The largest 

 spines on the middle-part of the ray are 10-20 n long and 2-4 n thick at the base. 

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

 18-32 fi, usually 20-30 n, on an average 23.6 m- The lateral rays of the same 

 spicule are usually fairly equal (Plate 42, fig. 35), sometimes considerably unequal 

 (Plate 42, fig. 36). They are 21-32 ^ long, straight, nearly cylindrical in their 

 basal part, attenuated toward the end in their distal part, and blunt-pointed or 

 terminally rounded. The proximal parts of the lateral rays are usually rather 

 smooth; their distal parts bear sparse small spines. A sixth proximal ray is 

 observed very rarely and, when present, is short and rudimentary. 



The dermal pinules of form B (Plate 42, fig. 29) are very similar but have 

 a shorter and more bushy distal rays and longer lateral rays. The distal ray 

 is 85-97 M long, on an average 93 fi, and 3.5-6 ^ thick at the base. Its maximum 

 transverse diameter, together with the spines, is 28-34 ai, on an average 29.2 fi. 

 The lateral rays are 25-30 n long. 



The dermal pinules of form C (Plate 42, figs. 20-23) are even more similar 

 to those of form A, but have a slightly more bushy distal ray and longer lateral 

 rays. The distal ray is 95-114 fi long, on an average 104.9 /i, and 4-6 ^ thick 

 at the base. Its maximum transverse diameter, together with the spines, is 

 22-32 fi, on an average 27 n. The lateral rays are 25-35 fi long. 



The dermal pinules of form D (Plate 42, figs. 30-34, 42) differ from those of 

 the other forms by the distal ray being not so long, having a shorter and stouter 

 terminal cone, and being covered with more numerous and crowded spines. 

 The distal rays of the dermal pinules of this form therefore appear, when com- 

 pared with those of the other forms, more stunted, stout, and dense. The distal 

 ray is 82-101 fi long, usually 87-95 fi, on an average 89.1 yu, and at the base 

 4.5-8 M thick, usually 4.5-6 fi. Its maximum transverse diameter, together with 

 the spines, is 23-32 yu, on an average 26.2 /j. The terminal cone is 8-1 1 n thick. 

 The lateral rays are 17-30 fi long, exceptionally up to 38 fi. 



The dermal pinules of form E have a distal ray 70-94 fi long, on an a^'erage 

 86.7 fi. Its maximum thickness, together with the spines, is 22-32 fi. The 

 lateral rays are usually 18-23 fi long. 



The dermal pinules of form F ha^'e a distal ray 85-97 n long, on an average 

 90 fi. Its maximum thickness, together with the spines, is 23-25 fi. The lateral 

 rays are usually 23-43 m long. 



