SPHAERECHINUS. 



451 



Japan ; China ; Australia ; New Zealand. 



(STRONG YLOCENTROTUS.) Sphaerechinus. 



Sphaerechinus Desor, 1857, Syn. Ech. foss. 



Test thick ; tubercles of uniform size, imperforate, not crenulate, nu- 

 merous, closely packed together upon both areas. Aetinal system decagonal, 

 with deep cuts. Buccal membrane thin, generally covered by four rather 

 prominent plates. In the poriferous zone the pores are arranged irregularly 

 in closed arcs of from four to eight pairs. 



This genus can hardly rank as more than a subgeneric division of Stron- 

 gylocentrotus ; the presence of deep, sharp cuts in the aetinal system and the 

 regularity of the arrangement of the tubercles, although giving to the 

 species of this genus a striking facies, are simply quantitative characters, 

 the value of which a better acquaintance with the subject will determine. 



Sphaerechinus Australiae 



'.Sphaerechinus Australiae A. Agass., 1872, Bull. M. C. Z., ILL 



PL VI. f. is. 



Test thick ; outline globular, especially in young specimens, in which the 

 outline resembles that of Amblypneustes, but as they grow older they be- 

 come somewhat flattened below. The poriferous zone is narrow ; the four 

 pairs of pores are arranged in arcs of three pairs towards exterior, well 

 separated from the inner fourth pair, — this is quite hidden among the tuber- 

 cles, forming almost an independent vertical row. There are two principal 

 vertical rows of primary tubercles in the ambulacral space on each side of 

 the median line, forming, with the two rows of smaller tubercles separating 

 the inner pair of pores from the others, oblique lines of tubercles from the 

 median line to the exterior edge of the poriferous zone. 



