38 Trans. Acad. Sci. of St. Louis. 



composed of nine columns each. Ambulacral areas half as 

 wide as the interambulacral. Pores circular, two to each 

 ambulacral piece, arranged in four vertical rows, the outer 

 rows more or less zigzag. Surface covered with granules, 

 about twenty-five to each larger interambulacral plate. 



Geological formation and locality: Keokuk Group, Jersey 

 Co., near Warsaw and Alton, 111.; Fenton, Curry ville and 

 Boonville, Mo. ; Keokuk, Iowa. 



2. Oligoporus coreyi Meek and Worthen. 



1870. Oligoporus Coreyi. Meek and Worthen, Proc. Acad. 



Nat. Sci. Phil., p. 34. 

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



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

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



263. 



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

 vol. 2, p. 183. 



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

 vol. 7, p. 186, pi. 6, fig. 25-29. 



Body small, globose. Interambulacra twice the width of 

 the ambulacra, composed of six columns each. Interambu- 

 lacral plates covered with small tubercles. Ambulacral areas 

 quite deeply furrowed. Pores of the ambulacral plates near 

 the outer edge. 



Geological formation and locahty: Keokuk Group, Craw- 



fordsville, Ind. 



3. Oligoporus missouriensis Jackson. 



1896. Oligoporus missouriensis. Jackson, Bull. Geol. Soc. 

 Amer., vol. 7, p. 184, pi. 9, figs. 50-52. 

 Interambulacral areas composed of six columns each. In- 

 terambulacral plates about five times as long as the ambulacral 

 and curving slightly at the junction with the ambulacral. 

 No accessory ambulacral plates. Each ambulacral plate pro- 

 vided with two pores. Ambulacral plates lying opposite the 

 horizontal sutures between the interambulacral plates spread 

 fan-shaped on the outer border. 



