PALEONTOLOGY OF IOWA. 541 



This species is distinguished by the gibbous base, which curves gently to the 

 central depression, and to the outer margins ; while the greater gibbosity of the 

 individual radial plates, and their contraction at the lateral margins give it the ap- 

 pearance of being much larger; so that when reversed, the base appears like a rounded 

 prominence set upon a larger pedestal. I have been disposed to refer this to P. bur- 

 lingtonensis ; but the pelvis or base is much larger in proportion to the body, and 

 the attachment for the column is relatively smaller. 



Geological formation and locality. In the Burlington limestone : Bur- 

 lington, Iowa. 



Platycrinus notlulosus ( n. s.). 



BASE broad, obtusely pentagonal, the centre abruptly de- 

 pressed for the reception of the column, moderately convex, 

 sloping towards the margins, and somewhat channelled or 

 doubly-bevelled near the upper edges ; lines of suture slightly 

 grooved. Radial plates somewhat heptagonal, gradually ex- 

 panding from the base, as wide at the top as the length of 

 the plate ; the articulation scarcely more than one-third the 

 width of the plate, wider than long, the upper margin 

 scarcely concave. 



SURFACE of base marked by one or two rows of rounded 

 pustuliform nodes inside the bevelled margin ; those directed 

 towards the angles most prominent, similar ones on the ra- 

 dial plate in converging lines from the outer basal angles to 

 the base of the arm, with others included between and out- 

 side of those, the whole arranged somewhat in concentric 

 lines. 



This species is clearly distinct from any other known to me in this rock, and may 

 be recognized in the basal pieces by the round, more or less prominent pustulose 

 processes, the abrupt depression in the centre, and the doubly bevelled edges of the 

 plates. 



Geological formation and locality. In the Burlington limestone : Bur- 

 lington, Iowa. 



