THE ECHINO1DEA 



FIG. XXXIII. 

 Heterocentrotus //mr</VMii.s (after Agassiz), showing relation of primary and secondary spines. 



FIG. XXXIV. 



Colobocentrotvs otratns, showing the tessellatc arrangement of the spines. 



XXXIV.). The spines of the Triassic genus, Anaulocidaris, Zitt., had 

 a similar arrangement. 



