188 PALEONTOLOGY OF ILLINOIS. 



Interradial plates of moderate size, resting on the corners of 

 the first radials. Anus in form of a simple subcentral opening 

 in the vault. The opening is very small, surrounded by a num- 

 ber of minute plates. 



Vault depressed-convex, composed of small, smooth plates. 

 It is conspicuously marked by five strongly elevated ridges, 

 radiating from the center to the armbases. They are composed 

 of small covering plates, which in the two posterior rays ex- 

 tend to the central plate, but in the others rest between the 

 proximals. There are two proximals at the anal side, but ap- 

 parently no special anal plate, or, if present, it is not distin- 

 guishable from the other small plates bordering the anal open- 

 ing. Nearly the same structure is found in a specimen of P. 

 truncatulus, in which two of the rows of covering pieces, at 

 least, extend to the central plate. 



Column short, large, rapidly twisted, composed of transverse 

 elliptic joints, as usually in the genus. It tapers to a point, and 

 near the end is provided Avith numerous short rootlets; which 

 taper in a similar manner. Perforation minute. 



Surface of plates and arms smooth, without any ornamenta- 

 tion. 



Geological position, etc. : Kinderhook beds of the Lower Car- 

 boniferous, LeGraiid, Iowa. 



Collection of Wachsmuth and Springer. 



PLATYCRINUS PLANUS Owen and Shumard (?). 



PL XVI Fig. 8. A specimen with arms. 



1860, Journ. Acad. Nat. Sci. Phila. (Ser. II.), Vol. II, p. 573. 



1852, U. S. Geol. Surv. Wise., Iowa and Minn., p. 587, PI. 5a, Fig. 4. 



1858, Hall. Geol. Surv. Iowa, Vol. II, Pt. II. p. 533. 



1868, Meek & Worthen, Geol. Surv. 111., Vol. Ill, p. 467. 



1873, Meek & Worthen, Ibid, Vol. V, PI. Ill, Fig. 5. 



The specimen figured under the above name belongs to a type 

 not uncommon in the LeGrand beds. It is larger and more 

 elongate than the preceding species, and characterized by a 

 rather low, gently swelling subturbinate basal disk, above which 



