580 Verrill, Notes on Radiata. 



below the periphery and extends nearly as high as the ])receding row, 

 usually ceasing about two plates sooner ; in young specimens this row 

 is wanting, and the large tubercles of the first row cease sooner ; out- 

 side of the first row of large tubercles there is another similar row of 

 secondary ones, commencing at about the same place, but extending 

 quite to the genital plates, as in the younger specimens ; the second 

 row of large tubercles extends about to the third plate above the 

 periphery ; the third ceases at or below the periphery ; the fourth 

 extends upward to within one or two plates of the apex of the yel- 

 low triangular area ; and the remaining rows cease successively sooner, 

 the two median rows scarcely rising above the periphery. The ac- 

 tinal membrane is filled with small, transversely oblong and elliptical, 

 imbedded plates, some of which bear one or two small and very slen- 

 der spines, which are more numerous on the larger plates near the 

 mouth. The spines of the lower surface are straw-color ; the larger 

 ones of the upper surface are tinged and banded with purplish at 

 base, the outer half straw-color ; the small ones are very slender and 

 mostly purplish throughout. 



The largest specimen from La Paz has the test 5*90 inches in diam- 

 eter ; 2-10 high ; diameter of actinal area 1 '50 ; of abactinal area 1*35 ; 

 of anal region .80; length of longest spines of upper surface 1*80. 



Echinodiadema coronatum Ven-iii (p. 295). 



In the Bulletin of the Museum of Comparative Zoology, i, p. 282, 

 1869, Mr. A. Agassiz considered this the young of Diadema Jlexi- 

 canum. On reexamining the original specimen and comparing it with 

 the genuine young of that species, he is convinced that it is really 

 quite distinct, both generically and specifically. 



The exist;pnce of spines on the actinal membrane (to which the 

 name refers) is of itself quiet sufficient to distinguish this genus from 

 the young of Diadeuia, in all stages of growth. In all the species of 

 the latter the actinal membrane in young specimens is covered with 

 pretty regular, nearly smooth plates, which later in life become more 

 separated and deeply imbedded, but never bear spines. 



The name, Echinodiadema, has more recently been used for an en- 

 tirely difierent genus by M. Cotteau (Rev. et Mag. de Zool., May, 1869). 



EchinOCidaris Dufresnii Desmoulins, Echin., p. 306. (p. 344). 



Echinocidaris Scythei Philippi, Wiegm. Arch., 1857, p. 131. 



According to Mr. Agassiz, who has seen the original specimen of 

 M Dtifresnii and others in the British Museum from Str. of Magellan 

 (coll. Cunningham), which are identical with M Scythei, this species 

 belongs to the fauna of Patagonia. 



