246 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



three being separated only by a very narrow ridge, carrying a series of 

 very small tubercles. The areoles are broad, transversely oval, and not 

 deepened. The median area is fairly broad, slightly more thanjhalf 

 as broad as the areoles. Outside the rather prominent scrobicular 

 ring there are several very small tubercles, not regularly arranged, 

 leaving a rather distinct bare median line, which is hardly atall 

 sunken. In the corner between each two areoles there may be, at 

 the ambitus, a single larger tubercle of the same size as those j}f the 



Fig. 



1.— Part of ambulacrum of Histocidaris magnifica, new 

 species. X7.5 



scrobicular ring. The adradial part of the interambulacral plates 

 carries outside the scrobicular ring some rather closely set smaller 

 tubercles, leaving, however, a conspicuous bare margin. 



The apical system is somewhat arched, in continuation of the 

 regular arching of the test. The ocular plates are deeply sinuate on 

 the outer edge, and are in contact with the periproct, excepting for 

 the two joining the large madreporic plate. The genital plates are 



Fig, 2.— Part of apical system of Histocidaris magnifica, new 

 species. X2.5 



narrow, with large genital openings, which lie entirely within the 

 plate. Tubercles are few, as is usual in this genus, being confined 

 mainly to the circumference of the genital pores, a single arched series 

 occurring proximally on the genital plates, and to a half circle along 

 the outer edge and one or two proximally on the ocular plates. The 

 periproctal plates are rather closely tuberculated. (Fig. 2.) The 

 peristome has not been examined in detail, as this could not be done 

 without doing harm to the splendid specimen. 



