NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER 5 



the coarser and fewer plates covering the ambulacral areas, there 

 being two rows of 5 or 6 plates to each ambulacrum, in contrast to 

 9 or 10 in Hall's species. All plates show a punctate structure. The 

 oral plates, one large and two small ones opposite it, are quite visible. 

 Interambulacral plates minute, nodose ; anal pyramid indistinct but 

 visible. 



Occurrence. — Cincinnatian (Eden shale-Economy beds), West 

 Covington, Kentucky. 



Hohtype.—U.S.NM. no. 42138. 



CINCINNATIDISCUS Bassler, 1935 



Species of this genus, formerly confused with Hemicystites, show 

 most resemblance to Cystaster except that the theca is depressed or 

 flat, attached by the whole basal surface, and the interambulacral 

 plates are squamose, imbricating distinctly, and surrounded by a mar- 

 ginal zone of small nodose plates. 



CINCINNATIDISCUS (HEMICYSTITES) STELLATUS (Hall), 1856 

 Plate 2, figs. II, 12 



This edrioasteroid, the type of the genus, is not so uncommon and 

 thus affords opportunity for the study of specific variations. Figure 1 1 

 on plate 2 shows that the number of rays may vary as in other genera. 

 The theca, averaging 8 mm in diameter, is attached, depressed, pen- 

 tagonal, with usually five straight, short, broad, club-shaped rays 

 bearing usually 12 covering plates, to a row, each plate being almost 

 as wide as long. Supraoral plates three, a large one opposite the 

 anal area, and opposite this two smaller ones. Anal pyramid of very 

 small nodose plates. Interambulacral plates imbricating, squamose, 

 the central ones larger, and the outer marginal ones smaller and 

 covered with small nodes. 



Occurrence. — Cincinnatian (Maysville-Fairmount and Bellevue for- 

 mations), Cincinnati, Ohio, and vicinity. 



Plesiotypes. — U.S.N.M. no. 42106. 



CINCINNATIDISCUS (HEMICYSTITES) CARNENSIS (Foerste), 1914 



Plate 5, fig. 4 



Theca discoidal, faintly pentagonal, 7 mm in diameter, with promi- 

 nent rays, subclavate in outline, similar to C. stellatus (Hall) but 

 differing in its narrower rays and correspondingly wider interam- 

 bulacral areas. 



