ECHIXOTHRIX. 413 



ECHINOTHRIX. 



Echinothrix Peters, 1803, Monatsb. Akad. Berlin. 



Peters first called attention to the differences of the ainbulacral system 

 existing in several species of Diadeinatidae referred by Agassiz to Astropyga. 

 Gray and Desor subsequently established the genera Garelia and Savignya 

 to include the same type. This genus combines the features of Diadema 

 and of Astropyga. It has more the general facies of Diadema, a high test, 

 moderately stout ; larger tubercles and fewer vertical rows than Astropyga 

 in the interambulacra ; the ambulacra, however, differing very materially in 

 having many vertical rows of very small tubercles in place of the larger 

 tubercles of uniform size which characterize both Astropyga and Diadema. 

 Their structure is the same with that of the large ones, however. The am- 

 bulacra also are much broader near the abactinal system, becoming petaloid 

 there ; the space between the two primary rows of small tubercles is filled 

 with tubercles of nearly the same size, forming irregular vertical rows, the 

 median ambulacral zone becoming very much broader than the poriferous 

 zone ; the reverse is the case on the actinal surface, where the poriferous 

 zone is broader than the median ambulacral space. The poriferous zone is 

 broad, and the pores are arranged as in Astropyga. At first glance the 

 spines of the two areas appear very different ; they are only of different 

 size, the structure is nearly identical, — the one being very fine elongated 

 silk-line spines, the other large verticillate or longitudinally striated spines, 

 not as hollow as in Diadema, but having more the solidity of those of 

 Astropyga. The anal system is strongly protected at the base by plates, as 

 in Astropyga. The abactinal system resembling that of Astropyga, but 

 plates not cpiite so elongate. There is no bare forked median interam- 

 bulacral space, as in Astropyga. 



Echinothrix calamaris 



Echinus calamaris Pall., 1774, Spie. Zool. 



lEchinothrix calamaris A. Agass., 1872, Rev. Ech., Pt. I. p. 120. 



PL IIP./. 1-2 ; PI XXXV. f. io-i5. 



This species is more closely related to E. Desorii, and is subject to consid- 

 erable variations in the proportions and size of the spines. Unlike the young 

 of E. turcarum, the spines of the young of this species are comparatively 

 shorter, but at the same time also proportionally much broader, more or 



