16 HAWAIIAN AND OTHER PACIFIC ECHINI. 



In a specimen 35 mm. in diameter, with six and seven primary inter- 

 ambulacral plates, the abactinal system measures 16 mm., the anal 10 mm., 

 the actinal 17 mm. 



The longest primary radiole of a specimen 30 mm. in diameter, with six 

 and six primary tubercles, measures 73 mm. 



The primary radioles (PI. 5, fig. 7) are somewhat swollen near the base, 

 and taper very gradually toward the tip (Pis. 27-30). The radioles are of 

 a grayish pink tint faintly banded transversely with darker, alternating with 

 lighter, colored patches. The shaft is covered with longitudinal rows of 

 low, blunt serrations. The base of the shaft above the milled rino- is of a 

 dark chocolate color. The same coloring extends to the secondary and 

 miliary spines. There is but little difference in the shape and proportion 

 of the primary radioles in the specimens collected. The radioles of the 

 smaller specimens are proportionally more slender (PI. 30). The small 

 actinal primary radioles are fluted and somewhat club-shaped (Pis. 27, 30, 

 fig. l). In large specimens the general aspect of the regular secondary 

 and miliary tuberculation of the test (Pis. 27-30) greatly resembles that 

 of Chondrocidaris, though the contrast between tlie secondaries of the 

 sci'obicular area and of the rest of the interambulacral plates is not as 

 marked- as in that genus, and is perhaps more as we find it in the test 

 of Stereocidaris. In smaller specimens (PI. 26, figs. S-8) the tubercles 

 of the interambulacral plates outside of the scrobicular circles are. less 

 uniform in size and less regularly arranged and carry small miliary spinelets. 



The median ambulacra! space is filled by two irregular vertical rows 

 of small secondaries (Pis. 27, 28, 29, fig. j). In smaller specimens the 

 median vertical rows are well separated and run close to the outer rows 

 of secondaries (PI. 26, fig. 8). 



The abactinal system of large specimens (PI. 28) is very uniformly 

 covered with secondaries. These are less prominent in smaller specimens 

 (PI. 26, fig. .5). 



The outer row of plates of the pentagonal anal system is made up of 

 large, irregularly shaped plates, the next and following rows of which there 

 are four or five, of smaller polygonal plates, which become smaller towards 

 the anal opening. 



In the actinal system there is but a single row of narrow interambulacral 

 plates (PI. 26, fig. 6'). In larger specimens they are split into three or four 

 rows (PI. 27.) 



