FOSSILS OF THE KEOKUK GROUP. 501 



and strongly beveled or excavated along the sutures on each 

 side, while the surface of each is ornamented with small, 

 irregular, wart-like nodes, similar to those on the base; 

 these sometimes coalesce into irregular ridges, but are 

 usually arranged in three rows, starting from the most 

 prominent upper end of the plates, and radiating to the 

 base; facet for the reception of the second radial pieces 

 about one-third the breadth of the upper end of the plates, 

 and somewhat excavated. Anal piece of much the same 

 size and general nodose appearance as the first radial on 

 each side, but somewhat longer, and having an irregular 

 hexagonal form. Second radial pieces small, about twice 

 as wide as long, and more or less quadrangular in form. 

 Third radials slightly larger than the second, with a pen- 

 tagonal form, the upper sloping sides supporting the first 

 division of the arms. Arms rounded, composed at first of 

 pieces about as long as wide, upon the second or third of 

 which they bifurcate, the outer divisions remaining simple, 

 and the inner ones bifurcating again on the second or third 

 piece, the outer division, as before, remaining simple, and 

 the inner bifurcating a third time on the second pieces, thus 

 making in the posterior rays (the only ones seen) eight 

 arms to each ray, or forty in the whole series, if other rays 

 have the same number. All the simple arms are long, 

 slender, rounded, and but slightly tapering; near their 

 bases they are each composed of a single series of somewhat 

 wedge-formed pieces, but gradually pass into a double 

 series of minute interlocking pieces. 



Breadth of body, 0.98 inch; hight, about 0.43 inch; length 

 of one of the simple arms, about 1.60 inches ; thickness of 

 same at base, 0.05 inch. 



Associated with the specimen from which the foregoing description 

 was drawn up, several other imperfect examples were found, differing 

 more or less in form and in the arrangement of their ornamentation, 

 which either indicate considerable variations in these characters, or the 

 existence of several allied species. One of these has the first radial and 



