INVERTEBRATES. 245 



Of the interradials, the first is about the size of the subra- 

 dials, hexagonal in form, and supports two smaller ones in the 

 next range. Above the latter the rays diverge considerably, 

 and it is evident there was at least a single row of small pieces 

 fitting into the notches between the ends of the primary radials, 

 but whether these curved up and connected with the vault, or 

 whether they connected with others filling the whole interra- 

 dial space between, our specimen is too imperfect to enable us 

 to determine, though we think the former was the case. 



Anal pieces, seven or eight known, very small, and showing 

 the peculiarity characterizing the group very clearly, the whole 

 range forming a little finger-like appendage about the size of 

 one of the smaller divisions of the arms. 



Column rounded and comparatively thick at its junction with 

 the base, from which it tapers gradually towards the lower 

 extremity ; near the base composed of extremely thin equal seg- 

 ments, connecting by crenulated sutures, the crenulations being 

 formed apparently by radiating strise on the surfaces of the seg- 

 ments ; farther down it gradually passes into a series of alter- 

 nately thicker and thinner pieces. 



Locality and position : Keokuk division of Subcarboniferous series; on the 

 river bluffs, near south line of Monroe county, Illinois. 



Onychocrinus Norwoodi, M, and W. 



PI. 17, fig. 3. 



Forbesiocrinus ? Norwoodi, Meek and Worthen, Sept., 1860. Proceed. Acad. Nat. Sci., 



Philad., p. 389. 

 Taxocrinus Norwoodi, Meek and Worthen, Aug., 1865. Proceed. Acad. Nat. Sci., 



Philad., p. 142. 

 Comp. Onychocrinus exculptus, Lyon and Cassedat, 1859. Am. Jour. Sci. xxix, p. 78. 



Body below the last primary radial pieces, apparently short 

 obconical, or expanding rather abruptly and regularly upwards 

 from the base; composed of nearly smooth, thick plates, con- 

 nected by linear sutures. Base small, consisting of very low, 



