PLATYCRINID^. 703 



very gradually tai^ering 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. 



EEIIISPEERICUS 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 hemispliericus M. and W. 

 Plate LXVI. Figs, la, b, c, cl. 



1865. Meek and Worthen ; Proceed. Acad. Nat. Sci. Pliila., p. 162 ; also 1866, Geol. Eep. Tllinnis, Vol. 



III., p. 511, Plate 20, Figs. %a, b. 

 1881. W. and Sp. ; Revision, Part II., p. 72 (Proceed. Acad. Nat. Sci. Pliila., p. 246). 



Calyx subglobose, rather large in proportion to the arms. Dorsal cup 

 bowl-shajDed, 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. Eadials 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 



