THE ECHINOWEA 



Fio. XXXIII. 

 Hcterocentrotitf mammillatus (after Agassiz), showing relation of primary and secondary spines. 



Fio. XXXIV. 

 Colobocentrotui atratug, showing tlie tessellate arrangement of the spines. 



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

 a similar arrangement. 



