HETEROCENTROTUS. 427 



kind of tubercles closely crowd over the upper coronal plates, and the whole of 

 the genital and ocular plates. Each coronal plate in the interambulacral zone 

 has two parallel rows of primary tubercles, as many as eight in each row: 

 in larger specimens, near the ambitus, these tubercles are small, with a well- 

 marked scrobicular circle, but a very slight mammary boss, and a broad but 

 not highly developed tubercle ; the rest of the plate is covered by mil- 

 iaries of uniform size closely packed together. In the ambulacral space the 

 two median vertical rows consist of somewhat smaller tubercles closely ar- 

 ranged with an outer row of half the number of large tubercles, as large as 

 those of the interambulacra, separating the base of the poriferous arcs. The 

 miliaries which fill the median space extend laterally, but irregularly, across 

 the extremities of the arcs of the poriferous zone. The anal system is small, 

 deeply sunken, covered by minute plates. The ocular plates are large, trian- 

 gular ; the genital plates rectangular, with a large genital opening deeply 

 notching the outer extremity of the plate. The genital ring is much broader 

 than in C. atratus, and the difference in size between the madeporic genital 

 and the other plates not so marked as in that species. The poriferous zone 

 above the ambitus is much narrower than in C. atratus; the arcs are well 

 closed round the tubercles separating them, and consist of from six to seven 

 pairs of pores most regularly arranged, not crowded out of place, as is so 

 constantly the case in C. atratus. 



Bonin Islands ; Australia. 



HETEROCENTROTUS. 



Heterocentrotus Brandt, 1835, Prod. Des. An. 



Test very thick, elongated, as in Echinometra ; in this genus and in 

 Podophora the longitudinal axis makes an obtuse angle with the anterior 

 axis, the madreporic body being on the left extremity of the longer axis. 

 The tubercles are massive, comparatively few in number, with smooth base, 

 and imperforate. Poriferous zone very narrow above the ambitus, with 

 pores arranged in long narrow arcs of numerous pairs, round the tubercles ; 

 below the poriferous zone widens much more than in Echinometra, becom- 

 ing broader than the interambulacral space ; the actinostome is very large, 

 the actinal cuts very slight ; the jaws relatively much smaller to size of 



