Klem — Revision of the Palaeozoic Palaeechinoidea. 39 



Geological formation and locality : Augusta Limestone, 

 Webb City, Mo. 



4. Oligoporus mutatus Keyes. 



1894. Oligoporus mutatus. Keyes, Mo. Geol. Surv., vol. 

 4, p. 126, pi. 15, figs. 4 a, b. 



1895. Oligoporus mutatus. Keyes, Proc. Iowa Acad. Sci., vol. 

 2, p. 183, pi. 18, figs. 4 a, b. 



Test large, spherical. Interambulacral areas broad, com- 

 posed of five columns of plates each. Ambulacra only about 

 half as wide, very convex, elevated centrally, with shallow 

 bordering furrows. Surface covered with fine spines. 



Geological formation and locality: Keokuk Limestone, 

 Keokuk, Iowa. 



5. Oligoporus nobilis Meek and Worthen. 



1868. Oligoporus nobilis. Meek and Worthen, Proc. Acad. 

 Nat. Sci. Phil., p. 358. 



1873. Oligoporus nobilis. Meek and Worthen, Geol. Surv. 

 111., vol. 5, p. 476, pi. 11, fig. 3. 



1874. Oligoporus nobilis. Loven, Kongl. Svens. Vetens. 

 Akad. Handl., Bd. 11, No. 7, p. 42. 



1889. Oligoporus nobilis. Miller, N. Amer. Geol. Pal., p. 

 263. 



1895. Oligoporus nobilis. Keyes, Proc. Iowa Acad. Sci., 

 vol. 2, p. 182. 



1896. Oligoporus nobilis. Jackson, Bull. Geol. Soc. Amer., 

 vol. 7, p. 198, pi. 6, fig. 35. 



Body large, subglobose. Interambulacra composed of five 

 columns of plates, moderately convex. Ambulacra nearly flat, 

 narrow, lanceolate, not furrowed, about two-thirds as wide as 

 the interambulacral areas. Two pores to each ambulacral 

 piece, forming four double rows. Entire surface ornamented 

 with coarse granules, from forty to sixty to each of the larger 

 interambulacral plates. 



Geological formation and locality : Burlington Limestone, 

 Calhoun Co., and Warsaw, 111. ; Keokuk, Iowa. 



