684 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



Platycrinus subspinulosus Hall. 

 Plate LXVI. Figs. 2a, h, and Plate LXX. Fig. 9. 



1860. Hall; Suppl. Geol. E.ep. Iowa, p. 81, witli diagrammatic figure. 



1881. W. and Sp. ; Revision, Part II., p. 75 (Proceed. Acad. Nat. Sci. Phila,, p. 249). 



Below medium size. Height of dorsal cup about equal to the width at 

 the lower edges of the radial facets, where the section is distinctly quinque- 

 lobate, owing to a thickening of the radials at the median line toward the 

 facets. Plates thin at their edges, but quite heavy at the middle ; covered 

 ■with short spines or con.spicuous nodes, which upon the basal cup are quite 

 irregularly distributed, some of them being thickly set and confluent, others 

 dispersed, especially in the upper portions of the cup. The spines upon the 

 radials are arranged in three rows, two of them proceeding from the facets 

 diagonally to the lower angles of the plates, the other vertically to the basal 

 cup. Interradial sutures at the bottom of a shallow angular depression, not 

 grooved ; interbasal sutures obsolete. 



Basal cup subcylindrical, a little widest at the upper end ; the column 

 facet projecting and distinctly elliptic. Radials slightly spreading, nearly 

 once and a half as long as wide ; the facets horse-shoe shaped, longer than 

 wide, profoundly excavated, and having a deep, rounded notch at the upper 

 end. Structure of arms and ventral disk unknown. 



Horizon and Locality. — Upper Burlington limestone, Burlington, Iowa. 



Tu2^e in the Illinois State Museum of Natural History. 



Platycrinus Davisi W. and Sp. (dov. spec). ' 

 Plate LXX. Fig. I4. 



Below medium size. Dorsal cup depressed bell-shaped, a little wider 

 than high, rounded at the base, the sides concave along the basal cup, con- 

 vex along the radials. Plates rather heavy ; the suture lines very slightly 

 grooved. 



Basal cup deep, wide at the bottom, its height equal to two thirds the 

 length of the radials, its lower face quinquelobate, having five short, rounded 

 nodes, interradially disposed and extending over the whole width of the 

 plates ; they are separated by a well defined groove, giving to the base the 

 appearance of being quinquepartite. Attachment for the stem circular and 



