~y~ 
HEX ACRINID A. 785 
completely within the radial facets; wider than long, sharply angular at the 
top, their sloping upper faces concave. Arms four to the ray, their structure 
unknown. Ventral disk highly elevated, resting upon the inflected upper 
ends of the radials and anal plate, and hence narrower than the dorsal cup; 
the sides almost vertical, and the summit flat. The posterior oral, which is 
subcentral, is large and strongly convex, the four others considerably nar- 
rower and almost flat; the outer ends of the latter curve abruptly down- 
ward, and take part in the sides of the disk. ‘The radial dome plates rest 
at right angles between two orals; they are quite large, and are extended 
into short, heavy obliquely directed spines. The first range of interradials 
consists of three pieces, of which the two outer ones are very narrow and do 
not touch the radials; they are followed by two small interambulacrals, and 
these by the orals. The anal plate supports upon its truncate upper face 
_a rather large quadrangular piece, and upon its upper sloping faces an elon- 
gate narrow one, followed by other rows of three plates of smaller size, and 
by a moderate number of other pieces, which form a small protuberance 
containing the anus. Anal opening on a level with the posterior radial 
dome plates. 
Horizon and Locahty.— Upper part of St. Louis group; Russellville, Ky.; 
Logan Co., Ky., and Flagpont, Va. 
The type specimen, formerly in Dr. Shumard’s collection, could not be 
found in the Museum of Washington University at St. Louis, and is probably 
lost. The specimens figured are from the collection of Wachsmuth and 
Springer. 
_ Remarks. —This species is readily distinguished from 7. cornigerus by the 
greater depression and tumidity of the dorsal cup, the constriction at the 
arm bases, the erect form of the disk, the narrowness of the anal interradius, 
and the comparatively small number of disk plates. 
