500 PALEONTOLOGY OF ILLINOIS. 



Dome composed of numerous plates of various forms 

 and sizes, most of which, however, are small, and all are 

 nearly or quite flat, excepting one large convex piece im- 

 mediately over the axil of each ray. A few of those in 

 the central region are also larger than the others, but not 

 distinctly convex. Opening small, and situated about half 

 way between the middle of the vault and the anal side ; 

 surrounded by small plates, which are not protuberant. 



Surface of body plates finely and beautifully granulo- 

 striate the striae showing a tendency to radiate from the 

 central region towards the sides of the plates. 



Hight of body and dome, 0.90 inch ; greatest breadth, 

 measuring across between the prominent arm-bases, 1.40 in. 



This species is about of the same size as A. Americanos of Roeiner, 

 (A. Tuberosus, Troost?.) but will be at once distinguished from that form 

 by its more depressed body, much smaller and flat dome pieces, and 

 its flattened instead of protuberant anal region. 



Locality and position Greene county, Illinois; from the Keokuk di- 

 vision of the Lower Carboniferous series. 



GENUS DICHOCKimiS, Munstcr. 

 DICHOCRINUS EXPANSUs, M. and W. 



PL 14, Tig. 1. 

 IHchocrinus expansus, MEEK and WORTHEN. Proceed. Acad. Nat. Sci., Phila., 1868, p. 344. 



BODY expanding rather rapidly from the facet for the 

 attachment of the column to the top of the base, and still 

 more rapidly from there to the top of the first radials, so 

 as to make the breadth at the latter point about twice the 

 hight. Base forming less than half the bight of the body, 

 somewhat basin-shaped, though narrow below, and orna- 

 mented with small, irregular, wart-like nodes, which show 

 some tendency to form three or four vertical rows or ridges 

 on each basal piece. First radial pieces comparatively 

 large, somewhat oblong in form, being longer than wide, 

 with the widest end above, all convex along up the middle, 



