PLATE 54 



Figs. I, la, 2. Stethacanthus prcscursor, n. sp., p. 169. 



1. Lateral view of spine, based on the two cotypes; natural size. 

 la. Cross-section at about one-third from apex; natural size. 



2. A nearly complete spine — the more perfect of the two cotypes; 

 natural size. E 1908. 



Fig. 3. Stethacanthus depressus (St. John and Worthen). Small spine, X 2. 

 E 2516, p. 170. (Original is an impression in sandstone, and the figure is from a wax 

 squeeze of it.) 



306 



