Explanation of Plate XY. 



Page 



Fig. 1. Archceocidaris biangulata 130 



la. Side view of spine. (Hare collection ) 

 lb. View of same from below. 

 Ic. InterambtilacTum plate. 



CarboDiferouB, Upper Coal Measures. 



Fig. 2. Archceocidaris megastylus 129 



2a. Spines and plates. (Hare collection ) 

 2b. Cross-section of ioterambtilacral plate. 

 Carboniferous, Upper Coal Measures. 



Fig. 8. Archceocidaris aculeata 130 



Spine. (Hare collection ) 

 Carboniferous, Upper Coal Measures. 



Fig. 4. Oligoporus mulatus 126 



4a. Type specimen. (Cox collection.) 

 4b. Ambnlacral plates (enlarged) . 

 Carboniferou-, Keokuk limestone. 



Fig . 5 Archceocidaris agassizi 127 



Spines and plates. (Keyes collection ) 

 Carboniferous, Barlington limestone. 



Fig. 6. Archceocidaris dininnii 130 



Spines (After White ) 

 Carboniferous, Upper Coal Measures. 



