12 HAWAIIAN AND OTHER PACIFIC ECHINI. 



primary radiolos of the actinal side (PI. 4, fig. <V) are somewhat club-shaped 

 and fluted at the extremity. 



The secondary interambulacral spines are spathiform, shghtly grooved 

 on the upper surface, and dehcately fluted. Tiiey are of a yellowish gray 

 tint, with a greeni.sh stripe extending from the tip towards the base of the 

 spine. The ambulacral spines are similar to the interambulacral, only 

 much narrower, longer, and more slender. 



In a specimen 34 mm. in diameter (Pis. 13, figs. 1,2; 14, figs. 1,2) 

 there are five and six interambulacral plates. In the larger plates the 

 scrobicular area is surrounded by a ring of large secondaries, which occupy 

 the whole of the plate both in the median row and along the outer edge of 

 the poriferous zone (PI. 14, figs. 1,2). In the smaller interambulacral plates 

 towards the actinal system the median zone is formed of three or four rows 

 of small secondaries, and larger secondaries flank the poriferous zone (PI. 13, 

 fig. ,?). Tlie median ambulacral zone is formed by two vertical rows of small 

 secondaries. The abactinal system is 17 mm. in diameter. The anal system 

 is pentagonal, with an outer row of larger plates inclosing two irregular rows 

 of smaller plates (PI. 13, fig. £?) ; when dry the anal system and the genital 

 plates are of a light-green color. The ocular plates are heart-shaped, with 

 few small secondaries; the genital plates are covered near the anal system 

 by a cluster of small tubercles; these carry short, sharp, flattened, minute 

 miliaries. The actinal system is 14 mm. in diameter, and shows twelve 

 narrow ambulacral plates, with a small secondary on each side of the 

 poriferous zone. There is only a single row of five interambulacral plates 

 occupying the space between the actinal ambulacral plates; on the edge of 

 the interambulacral plates are very minute miliaries. The central part of 

 the madreporic genital is riddled with tlie madreporitic openings. 



In a specimen 29 mm. in diameter (Pis. 13, figs. 3,Jf; 14, figs. 3, If) 

 the abactinal system measures 15 mm., and the actinal 12 mm. in diameter. 

 There are five and five primary interambulacral tubercles. There are no 

 important differences in the test of this smaller specimen as compared with 

 that of the larger one. The principal dilYerence to be noticed is the absence 

 of miliaries and secondaries on the abactinal system. The genital and ocular 

 plates are nearly bare ; a few miliaries only are scattered on the proximal 

 part of the genital plates. 



In the smallest specimen collected, measuring 12 mm. in diameter (PI. 14, 

 figs. fJ-8), the abactinal system was 7 nnn. and the actinal 6 mm. There 



