IOWA ACADEMY OP SCIENCES. 
183 
Oligoporus mutatus Keyes. 
OUgoporus mutatm Keyes, 1894; Missouri Geol. Sur., vol. IV, 
p. 126, pi. XV, figs. \a-h. 
Test rather large, spherical, lobed. Interambulacral areas 
rather broad, moderately convex, composed of five vertical 
ranges of large hexagonal plates. Ambulacral areas less than 
one-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 lime- 
stone : 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 inter- 
ambulacral areas there are only five instead of nine vertical 
rows of iDlates. 
Oligoporus coreyi Meek & Worthen. 
Oligoporus coreyi Meek & Worthen, 1870; Proc. Acad. Nat. 
Sci., Phila., vol, XXII, p. 34. 
Like 0. dance but smaller, more depressed; ambulacra more 
deeply furrowed; only six rows of interambulacral plates 
instead of eight, and larger in proportion to the size of the 
test. 
Horizon and localities. Lower Carboniferous, Keokuk shales; 
Crawfordsville, Indiana. 
Nothing is known of this species beyond the original diag- 
nosis, the salient points characterizing it being given above. 
This description was a preliminary one and the revised account 
never appeared in the Illinois reports, as was customary with 
the species described by the authors. 
Oligoporus parvus Hambach. 
Oligoporus parvus Hambach, 1884; Trans. St. Louis Acad. Sci., 
vol. IV, p. 550, pi. C, fig. 3. 
Oligoporus parvus Keyes, 1894; Missouri Geol. Sur., vol. IV, 
p. 127. 
Like 0. dance but somewhat smaller. 
Horizon and localities. Lower Carboniferous, St. Louis lime- 
stone: St. Louis, Missouri. 
