34 HAWAIIAN AND OTHEE PACIFIC ECHINI. 



miliaries on the plates forming the angles of the pentagonal anal system. 

 Tlie proximal part of the madreporic genital is riddled with pores. The 

 genital openings arc large (a female PI. 18, fig. /) and placed near the 

 distal edge of tlie genital plates. The actinal s\-stem (PI. IS, fig. ;?) is pen- 

 tagonal, 2-") mm. in diameter, with eight rows of ambulacral plates, and not 

 more than four or five small interambulacral plates. The latter are bare 

 or carry one indistinct miliary. The ambulacral plates carry minute secon- 

 daries on the actinal edge of the plates. 



In a specimen 36 mm. in diameter (PI. 23, figs, l-j^) and 20 mm. in 

 height, there are six and seven interambulacral plates. The abactinal 

 system is circular, IG nun. in diauieter (PI. 23, fig. l); it differs only in si/e 

 from the structure of the abactinal system of the larger specimen described 

 (PL 18, fig. y), and being that of a male it has suiall genital openings. 

 A comparison of the interambulacral plates of the s[)eciuiens figured on 

 Plate 18 with those of PI. 23, figs J, ,^, shows that the ecjuatorial increase 

 of the test takes place more rapidly than the increase in width of the 

 median interambulacral zone covered by secondaries and miliaries. In 

 the smaller specimen there is only one circle of secondaries round the 

 scrobicular area, with a few irregularly arranged large miliaries filling the 

 angles of the interand)ulacral plates along the median line. The actinal 

 system is pentagonal (PI. 23, fig. 2) 1-1 mm. in <liameter. There are but 

 five rows of andtulacral plates with three or four ssmall elongated plates in 

 the suiall interamlndacnd space, four of the rows of ambulacral plates being 

 in contact alont^ the iuterandjulacral line, and leaving but a small auiile for 

 the interandjulacral actinal plates. 



In the specimen 22 mm. in diameter and 14 nun. in height, there are 

 six interambulacral plates. In the smallest specimen, 4.5 nun. in diameter 

 and 3 mm. in height, there are already four and five interambulacral plates. 

 The longest primary radiole is 14 nnn. The secondaries are few in number 

 and are more or less cylindrical or club-shaped. The abactinal system 

 is very large, 2.5 mm. in diameter, and each genital plate carries a con- 

 spicuous perforate tubercle. The actiuostome is less than 2 mm. in diauu'ter 

 and is jjractically covered by the ten buccal plates, a pair in each am- 

 bulacrum. The pedicellariiB are already- conspicuous, and, like the priiuary 

 radioles, are strikingly similar to those of the adult. In specimens of /'. 

 C<ib(j^i slightly larger, the structure of the abactinal system is very similar 

 to that of this young individual. 



