ol2 PALAEONTOLOGY OF ILLINOIS. 



subradial plates heptagonal in outline, instead of only one, as is usual in that 

 genus. So far as can be determined from our specimen, there seems to be 

 almost, if not quite, as much reason for placing it in the genus Poteriocrinus. 

 Yet it differs from the typical species of that genus, in having none of its first 

 radial plates resting directly upon a truncated upper side of one of the subra- 

 dials, as well as in having but one, instead of two, anal plates between the first 

 radials. We suspect when better specimens are found, showing all its charac- 

 ters, that it may prove to belong to an undescribed genus. It is not nearly 

 related to any other species with which we are acquainted. 



Locality and position: Sugar Creek, Sangamon county, Illinois; upper part 

 of Coal Measures. 



Genus ZEACRINUS, Troost. (See page 185.) 

 Zeacrinus discus, M. and W. 



PI. 26, figs. 3 a, 3 6. 



Zeacrinus discus, Meek and Worthen, September, 1860. Proceedings Acad. Nat. Sci., 

 Philad., p. '390. 



Body, below the summit of the first radial pieces, much de- 

 pressed, or subdiscoidal, about three times as wide as high, 

 composed of smooth, very slightly convex plates, which are 

 connected by moderately distinct sutures. Base very small, 

 fiat and pentagonal; columnar facet equaling about two-thirds 

 the diameter of the base, round, concave, and marked by dis- 

 tinct radiating striae; perforated by a round, minute, central 

 aperture. Subradial plates extending nearly horizontally out- 

 ward from the base, so as to form a distinctly pentagonal star- 

 shaped disc, all curving a little upwards towards their outer 

 extremities ; three of them pentagonal and two hexagonal, 

 each of the latter 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 truncated above, the upper side being 

 longer than either of the others. Second radials and succeed- 

 ing parts above, unknown. 



