5IO 



NORTH AMERICAN INDEX FOSSILS. 



Fig. 1824. a, d, Scaphiocrinus crineus ; c, d, S. subcarinatus ; nat. size and en- 

 larged ; e, DecaJocrinns pleias ; f, D. cegina. (After Hall and Whitfield.) 



XVII. ScYTALOCRiNus Wachsmuth and Springer. 

 Dorsal cup usually deep. Arrangement of plates as in Scaphio- 

 crinus, but the arms are stronger and remain undivided after the 



first bifurcation, above the first 



.-•^'^^^^ 



Fig. 1825, Scytalocrinus robustus, X/ 

 (After Worthen.) 



or second brachial. Pinnules 

 long and close. Mississippic. 



41. S. robustus (Hall). (Fig. 

 1825.) Mississippic. 



Calyx spreading more abruptly 

 from the top of the B than below. 



Keokuk of Indiana and Il- 

 linois. 



XVIII. Decadocrinus Wachs- 

 muth and Springer. 

 Dorsal cup very short, con- 

 cave at bottom. Arrangement 

 of plates as in Poteriocrimis, but 

 arms simple, thinner and com- 

 posed of long, cuneate joints, 

 which give them a strongly zig- 



