390 PROCEEDINGS OF THE ACADEMY OP 



The arms above the first division on the fourth and fifth radials, consist of 

 a single series of pieces, are rounded on the outside, and a little broader than 

 their diameter at right angles to their outer surface. One of them is seen to 

 bifurcate again on the sixth piece, and another on the eighth, beyond which 

 they are not known to divide again. Between each two of the arm pieces, as 

 well as the primary radial plates, the minute accessory patelloid pieces, 

 pointed out by Prof. Hall in other species of this genus, are distinctly seen. 



The column is comparatively large, near the body, tapers a little down- 

 wards, and is composed, for a short distance below its connection with the 

 base, of extremely thin segments, which fit together by distinct interlocking 

 crenulations around the margins ; and a little farther down they gradually 

 become alternately thicker and thinner. A transverse section shows the 

 central cavity to be comparatively large, and distinctly pentapetalous as thus 

 seen. 



Height from the base to the top of the first radials 0-19 inch; do. from base 

 to top of fifth radials 0*41 inch; breadth at the summit of the first radials 0*35 

 inch; breadth of base - 15 inch. 



Locality and position. Hardin County, Illinois. St. Louis Limestone of 

 subcarboniferous series. 



Genus ZEACRINUS, Troost. 



Zeacrincs discus. Calyx below the summit of the first radial plates small, 

 subdiscoidal, or depressed, basin-shaped, about three times as wide as high. 

 composed of smooth, very slightly convex plates, which are connected by mode- 

 rately distinct sutures. Base small, flat, aud pentagonal ; columnar facet 

 equalling about two-thirds the diameter of the base, round, concave, and 

 marked by distinct radiating stria?, perforated by a round, minute central 

 aperture. Subradial plates extending nearly horizontally outward from the 

 base, so as to form a distinct pentagonal, star-shaped disk, all curving a little 

 upwards towards their outer extremities; three of them pentagonal, and two 

 hexagonal, in consequence of each having one angle slightly truncated by the 

 anal pieces. First radial plates about twice as large as the subradials, rather 

 more than half as long as wide, pentagonal, and all transversely truncate 

 above, the upper side being longer than either of the inferior sloping ed^es, 

 which are longer than the lateral margins. 



The first anal plate is elongate pentagonal, and wedged down between one 

 of the subradials, and the inferior sloping side of one of the first radial plates, 

 its lower extremity resting upon a very short side of another subradial. Of 

 the second anal pieces there are two, one of which stands upon the short trun- 

 cated superior side of one of the subradials, and is supported on its right in- 

 ferior sloping side by the first anal piece, and on the left by one of the first 

 radials; the other stands upon the upper end of the first anal piece, being also 

 partly supported on the right by one of the first radial plates, and on the left 

 by the other second anal piece. Both the second anal plates project about 

 half their length above the summit of the first radials. (Remaining parts un- 

 known.) 



Height to the summit of the first radial plates, 0-17 inch ; breadth 0-46 inch ; 

 breadth of base 0-14 inch. 



Locality and position. Sangamon county, Illinois. Upper Coal Measures. 



Zeacrinus Teoostanus. Body rather small, depressed, basin-shaped below 

 the arms, somewhat rounded and concave on the inner side, composed of ap- 

 parently smooth plates, which are connected by linear sutures. Base verv 

 small, concave, and nearly or quite hidden by the column. Subradial plates 

 unequal in size, a little wider than long, excepting the one on the anal side, 

 four of them pentagonal, and one, which is longer than the others, heptagonal, 

 (counting the part of each connecting with the base, as one side.) First 

 radials nearly twice as wide as high, pentagonal, the superior horizontally 

 truncated edge being longer than either of the inferior sloping sides. Second 



[Sept. 



