128 BCHINODERMS. 



Archeeocidaris shumardana Hall. 



Archceocidaris shumardana Hall, 1858: Geol. lowa, vol. J, p. 699, pi. xxvl, 

 jags. 3a-d. 



Spines and plates as in A. agassizi, but only about one- 

 third as large. 



Horizon and localities. — Lower Carboniferous, Keokuk 

 limestone : La Grange (Lewis county). 



Archseocidaris keokuk Hall. 



Archceocidaris keokuk Hall, 1858: Geol. Iowa, vol. I, p. 699, pi. xxvl, figs. 

 2a- b. 



Known only from fragments. Plates with the marginal 

 nodes more prominent and further apart than in A. agassizi, 

 and the central tubercles also smaller. Spines less than two- 

 thirds the size of those of the species just mentioned. 



Horizon and localities Lower Carboniferous, Keokuk 



limestone: Clark county (apparently) ; Warsaw (Illinois). 



Archaeocidaris wortheni Hall. 



Plate xvi, fig6. Sa-b. 

 Archceocidaris wortheni Hall, 1858 : Geol. Iowa, p. 700, pi. xxvl, figs. 4a-g. 



Test subglobose. Interambulacral areas made up of four 

 rows of large hexagonal plates ; central tubercle about half as 

 broad as the plate, with the boss moderately elevated ; sur- 

 face of the plates glabrate except at the borders when the mar- 

 ginal row of nodes is quite narrow. Ambulacral area narrow, 

 about half as wide as the large hexagonal ossicles, composed 

 of rectangular plates, which are about twice as wide as high 

 and have a pair of large oval pores, about 10 occupying the 

 height of an interambulacral piece. Spines rather small, slen- 

 der, slightly curved, with an apparently smooth or finely gran- 

 ular surface ; below expanding rapidly into the broad crenulated 

 annulation. 



Horizon and localities. — Lower Carboniferous, St. Louis 

 limestone : St. Louis. 



