Explanation of Plate XVII. 



Page 

 Fig. 1. Melonites mulHpora 125 



la. Ambalacram (enlarged). 



lb. Apical disk (pularged). 



Ic. iQterambulacral plate (enlarged) . 



Carboniferous, Saint Louis limestone. 



Fig. 2. Oligoporus dancB\ 126 



2a. Ambulacral plates (enlarged) . 

 2b. IQterambulacral plates (enlarged). 

 Carboniferous, Keokuk limestone. 



Fig. 3. Archceocidaris wortheni 128 



3a. Ambulacral plates (enlarged). 

 3b. Interambnlacral plates (enlarged). 

 Carboniferous, Saint Louis limestone. 



