538 PALAEONTOLOGY OF ILLINOIS. 



with the spaces between the rather prominent pseudo-am- 

 bulacral areas almost flat near the middle, and more or 

 less concave belo\v. Base about even with the most promi- 

 nent part of the lower ends of the radial pieces, nearly flat, 

 and very distinctly pentagonal, or almost pentapetalous in 

 outline. Radial pieces forming about three-fourths the 

 actual hight of the body, abruptly incurved below to con- 

 nect with the base, and all divided quite to the loAver side 

 of the body by the pseudo-ambulacral areas. Interradial 

 pieces of moderate size, or about one-third as long as the 

 body, measuring over the curve of the sides from their 

 upper ends to the base; triangular in form and nearly as 

 wide as long, all strongly incurved above ; anal piece shorter 

 than the interradials below the anal opening. Pseudo-am- 

 bulacral areas rather narrow, tapering slightly from above, 

 and nearly as convex as the margins of the radials on each 

 side. Pore pieces about twenty-five to thirty on each "side 

 of the mesial furrow of each area; supplementary pore 

 pieces unknown; lancet pieces apparently not showing ex- 

 ternally. Summit depressed in the middle; central and 

 anal openings comparatively rather large ; so-called ovarian 

 pores of moderate size, situated one on each side of the 

 inner end of each interradial piece, and of course two 

 others as usual opening into the anal aperture. 



Surface apparently quite smooth, even as seen under a 

 magnifier, but probably when entirely unworn marked by 

 microscopic longitudinal striae. 



Hight of one of the largest specimens, 0.21 inch ; breadth, 

 0.23 inch ; breadth of pseudo-ambulacral areas, 0.04 inch ; 

 do. of spaces between the same, at the widest part, 0.13 inch. 



This little species is so A r ery clearly distinct from all others known to 

 us that it is unnecessary to compare it with any of those yet described. 

 Its most characteristic features are its small size, smooth surface, flat 

 space between the pseudo-ambulacral areas, and nearly even pentape- 

 talous base. 



We have before us nine specimens, of various sizes, all agreeing in 

 the characters givtsii excepting one, which, from abnormal development, 



