564 PALAEONTOLOGY OF ILLINOIS. 



little smaller than the first, nearly twice as wide as long, 

 pentagonal in form, with lateral margins short and not 

 constricted; each supporting two arms on its superior 

 sloping sides. Arms rather slender for species of this 

 genus, not being wide enough to be in contact laterally all 

 around, when raised vertically ; rounded on the dorsal side, 

 rather rapidly tapering, and, so far as can be seen in the 

 typical specimen, all bifurcating on the second piece ; below 

 the bifurcation the two pieces are each about as long as 

 wide, the upper one being sometimes slightly constricted 

 around the middle; arm piece above the bifurcation rather 

 slender, longer than wide, rounded, and distinctly con- 

 stricted around the middle. First anal piece about twice 

 as long as wide, and wedged so far down under one side of 

 one of the first radials by the side of the largest subradial, 

 as to come nearly or quite in contact with the very 

 small base. Second anal small, and resting upon the 

 short upper end of the larger subradial between the 

 upper part of the first anal on the right and the first 

 radial on the left; above these the alternating series con- 

 tinues up to connect with the ventral extension. Ventral 

 prolongation, or so-called proboscis, about equaling the 

 apparent length of the arms, comparatively rather nar- 

 row and sub-cylindrical below, but widening rather grad- 

 ually upward above the summit, where it flares suddenly 

 out all around to about the breadth of the body below, 

 its top being nearly flat, or much depressed, and com- 

 posed of small, unequal, convex pieces, while each one 

 of the marginal row of these top pieces, all around, extends 

 horizontally outward in the form of a sharp spine about 

 two-thirds as long as the entire transverse diameter of the 

 flattened top itself. Plates forming the sides of the ventral 

 portion below its flattened spiniferous crown, probably 

 more or less costated, or sculptured, in perfect examples, 

 but the specimen seen is not in a condition to show this, 

 though the usual pores can be seen passing through the 



