476 PALAEONTOLOGY OF ILLINOIS. 



ONYCHASTER BARRISI, Hall, sp. 



PL 10, Fig. 1. 

 Protaster Barrissi, HALL, 1861. Desc. New Crin., Prelim. Note. p. 18. 



Locality and position Burlington division of the Lower Carbonifer- 

 ous. Burlington, Iowa. Mr. WACHSMUTH'S collection. 



GENUS OLIGOPOKUS, Meek and Worthen. 

 OLIGOPORUS NOBILIS, M. and W. 



PI. II, Fig. 3. 

 Oligoporus nobilis, MEEK and WOKTHEN. Proceed. Acad. Nat. Sci., Phila., 1868, p. 358. 



BODY large, globose, composed of very thick plates. 

 Ambulacra nearly flat or slightly convex, and without 

 proper furrows, narrow lanceolate in outline, or only 

 about two-thirds as wide as the interambulacral areas; 

 pore pieces comparatively small, wider than high, those of 

 the two outer rows rather more irregular in size, and some 

 of them a little larger than any of those of the two inner 

 rows; pores two to each piece, forming four double rows, 

 those of the two outer ranges of pieces being placed near 

 their inner ends, and those of the inner ranges near their 

 outer ends. Interambulacral areas comparatively large, 

 moderately convex, and composed of five rows of large 

 plates, all of which extend to the disc above, while the 

 middle one ends within about 0.65 inch of the oral opening 

 below. Vent and apical disc much as in Melonites multi- 

 pora. Surface of all the plates, both ambulacral and inter- 

 ambulacral, ornamented with coarse granules, separated by 

 spaces generally a little wider than their own breadth, with 

 sometimes a few smaller ones between. Of these granules, 

 about forty to sixty may be counted on each of the larger 

 interambulacral plates. 



Hight and breadth, about 3.73 inches; breadth of ambu- 

 lacral spaces, 0.60 inch; do. of interambulacral areas, 1.06 



