r 
» 
PLATYCRINIDZ. ) 703. 
very gradually tapering upward, and covered throughout their full length 
with granules, similar to those upon the dorsal cup, but smaller. Structure 
of the ventral disk unknown. ; 
Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 
Type in the (Worthen) Illinois State collection. 
HEMISPHERICUS GROUP. 
Calyx to the arm bases more or less cup-shaped; the sides slightly 
spreading; the plates covered with distinct nodes, Arms of moderate size. 
Platycrinus hemisphericus M. and W. 
Plate LX VI. Figs. 1a, 6, ¢, d. 
1865. Mesx and Wortuen; Proceed. Acad. Nat. Sci. Phila., p. 162; also 1866, Geol. Rep. Ilnois, Vol. 
TII., p. 511, Plate 20, Figs. 2a, 6. 
1881. W. and Sp.; Revision, Part IL, p. 72 (Proceed. Acad. Nat. Sci. Phila., p. 246). 
Calyx subglobose, rather large in proportion to the arms. Dorsal cup 
bowl-shaped, twice as wide as high, the bottom excavated for the reception 
of the column. Basi-radial and interradial sutures slightly depressed but 
not grooved. Surface of plates covered with rounded, rather large and 
prominent nodes. There are generally five rows of such nodes at the 
base, three or four to each row, which pass out from the column facet 
to the upper angles of the plate, forming triangles, which are filled by 
additional nodes. From the radial facets two other rows of nodes pro- 
ceed to the lower angles of the radials, which are triangularly arranged 
like those upon the base, and these also enclose a variable number of 
similar nodes. The sides of the plates are covered with smaller nodes of 
irregular arrangement. 
Basals forming a shallow basin with a slight depression at the lower end ; 
the interbasal sutures indeterminable. Radials subquadrangular, wider than 
long, moderately expanding in width upwards; the upper faces at the sides 
of the facets very slightly sloping, except at the anal side where they form 
a broad and deep notch. Facets horse-shoe shaped, occupying one third the 
width and height of the plates; directed obliquely upward; the face con- 
cave; the upper end deeply notched. Costals very small, trigonal. Dis- 
tichals free above the first, which is very short; the second a little longer. 
Palmars, and post-palmars when present, as long as, or longer than, the 
cr 
= B 
