MUSEUM OF COMPARATIVE ZOOLOGY. 19 



in width towards the abactinal region, where it is slightly petaloid. Porif- 

 erous zone broad. Spines of intcrambulacra equalling in length two thirds 

 of the diameter of the test ; polar diameter depressed. This species may 

 be the Echinolhrix turcarum of Peters, which is undoubtedly a Garelia, and 

 not an Echinothrix. — Kingsmills and Sandwich Islands. 



Echinothrix Pet. Seeig. v. Moss, (emend.). — Savignya Des. Svn. 



This genus has been restricted in such a manner, that the species, such 

 as Diadema suhulare Ac, D. turcarum Rumph., placed by Peters in this 

 genus, have been removed to the genus Garelia of Gray, containing species 

 which can at once be distinguished from Echinothrix by their short and 

 longitudinally striated spines, while the genus Echinothrix, as limited here, 

 contains species having broad ambulacra, and spines resembling those of 

 Diadema. 



Echinothrix artnellata Pet. Seeig. v. Moss. —Zanzibar. 



Echinothrix aperta A. Ag. 



Eight rows of large tubercles in interambulacral space ; bare space of 

 interambulacrum extending below the equatorial line of test. Anal mem- 

 brane very large ; genital and ocular plates small ; anal plates very small, 

 disconnected. The spines vary much in color ; in some specimens they 

 are yellowish, in others perfectly black, in others whitish mixed with black. 

 — Society Islands. 



Echinothrix scutata A. Ag. 



Ambulacra more pointed towards the abactinal region than in the preced- 

 ing species. Spines shorter and more slender in proportion to the test. Can 

 at once be distinguished by the large size of the genital and ocular plates, 

 and the coating of prominent plates over the greater part of the anal mem- 

 brane, which is quite small. One row of small tubercles extending along 

 the poriferous zone in interambulacral space. — Sandwich Islands. 



Diadema Gray, Ann. Phil. 1828. 

 Diadema antillarum Piul. Wieg. Archiv. 1845. — Florida. 



Syx. Cidaris diadema Lamk. An. s. Vert, (non Diadema turcarum 



PiUMFH.). 



Diadema Savignyii Mich. Gue'r. Mag. Zool. 1845; Ag. Cat. Pais. 1847.— 

 Zanzibar. 



Diadema paucispinum A. Ag. 



Outline, when seen from above, pentagonal ; ambulacra very prominent, 

 large openings for suckers, poriferous zone narrow near actinostome. Cuts 

 of actinal system deep. Interambulacral tubercles arranged in six rows, 

 four large and two small median rows ; high coronal plates, which gives this 

 species the appearance of being but sparingly covered with spines; spines 

 stout, equalling in length diameter of test. — Sandwich Islands. 



