200 HAWAIIAN AND OTHER PACIFIC ECHINI. 



The pores on the abactinal surface are arranged in a double series on 

 each side of the ambulacrum, but the outer series contains fifty per cent 

 more pores than the inner, and a quincunx arrangement is seldom visible 

 (PI. 89, fig. 4). The greater part of the actinal surface, especially about 

 the actinostome, is closely covered with small tubercles of more or less 

 uniform size (Pis. 88, 89, fig. 1), giving an appearance not wholly unlike 

 Chcetodiadema ; this is most marked in large individuals. 



The actinal system (PI. 89, fig. l) is well covered by about eight con- 

 centric series of narrow plates, each carrying one row of small secondaries ; 

 the plates decrease rapidly in size adorally and leave small bare areas 

 between the adjoining ambulacra close to the mouth. 



-In the abactinal system (PL 89, fig. 2) the ocular plates are compara- 

 tively small, with distinct pores, and each carries two or three miliaries or 

 secondaries. In the specimen figured three of the genital plates are well 

 limited, and each carries from two to six small secondaries and miliaries. 

 With the other genitals, one cannot separate the plates of the anal system 

 from those which may be small proximal parts of the genital plates. The 

 genital pore is about in the centre of an elongate rectangular membrane 

 extending well down between the columns of abactinal interambulacral 

 plates. There are three to five rows of irregularly shaped small anal 

 plates, each carrying one or two small secondaries or miliaries. 



The coloration of this species is rather variable, for while most of the 

 specimens are more or less decidedly violet or purple, some large ones are 

 distinctly gray or yellowish-brown ; the plates, at least abactinally, are 

 frequently quite plainly outlined in a shade darker than the rest of the 

 test. 



The pedicellariae are abundant and rather characteristic. No ophicepha- 

 lous pedicellariae were found. The tridentate pedicellariae (PI. 65, figs. 4, 5) 

 occur everywhere and in very diverse sizes. The stalks (PI. 65, fig. 7) are 

 usually twice the length of the head, and may be three or four times as 

 long. The valves (PI. 65, figs. 6, 9, 10) are slender, often very slender, 

 compressed, in contact distally, and usually well separated at the base ; 

 the lateral margin is broadly curved where the blade joins the base 

 (fig. 10) ; much more rarely the blades are in contact for most of their 

 length, and the lateral margins are abruptly curved in (fig. 9) where the 

 blade joins the base. The valves range in length from half a millimeter 

 to nearly three millimeters. 



