126 ECHINODERMS. 



within the peristome of some specimens. The surface of the 

 test is covered by numerous small granules, which support the 

 spines, about 30 occupying each interambulacral plate. 



Horizon and localities Lower Carboniferous, St. Louis 



limestone : St. Louis. 



Melonites crassus Hambach. 



Melonites crassus Hambach, 1884 : Trans. St. Louis Acad. Sci., vol. IV, p. 

 548, pi. C, fig. 1. 



Closely resembling M. multipora, but with only five rows 

 of interambulacral plates, the latter being also larger and cov- 

 ered with larger spines. 



Horizon and Localities. — Lower Carboniferous, St. Louis 

 limestone : St. Louis. 



Oligoporus mutatus Sp. Nov. 



Plate XV, figs. 4a -b. 



Test rather large, spherical, lobed. Interambulacral areas 

 rather broad, moderately convex, composed of five vertical 

 ranges of large hexagonal plates. Ambulacral areas less 

 than half the width of the interambulacral, very convex or 

 sharply angular ; pore-plates small, very low, but wide, in four 

 rows, the median pair being about twice as wide as the outer 

 ones. Surface covered by small spine tubercles. 



Horizon and localities —Lower Carboniferous, Keokuk 

 limestone: Keokuk (Iowa). 



As distinguished from 0. dance, this form is somewhat 

 smaller in size, with the ambulacral areas much more elevated 

 centrally and the bordering furrows much more shallow. In 

 the interambulacral areas there are only five instead of nine 

 vertical rows of plates. 



Oligoporus danae (Meek & Worthen). 



Plate xvii, figs. 2a-b. 



MeZoTzzites rfa«cB Meek & Worthen, 1860: Proc. Acad. Nat. Sci., Phila., 



p. 397. 

 Oligoporus dance Meek & Worthen, 1866: Geol. Sur. Illinois, vol. II, p. 



249, pi. xvii, fig. 8. 



