700 THE CEINOIDEA CAMEEATA OF NORTH A21EEICA. 



set, bead-like processes, which give to the ridges a somewhat serrated aspect. 

 Suture lines obscure. 



Basals large, occupying two fifths to one half the height of the dorsal 

 cup, their lower ends projecting into a salient margin; their surface covered 

 with eight ridges, six of them radiating from the column to the six salient 

 angles which form the upper margin of the dorsal cup ; the two others 

 follow the interbasal siiture. Eadials as long as their width at the top, the 

 median portions obtusely angular, projecting outward, especially in the 

 upper part, where the outer margins of the plates form a depression or 

 groove along the interradial sutures; the outer edges of the facets sur- 

 rounded by a large, quite prominent, thickened rim, from which two ridges 

 pass out to the lower angles of the plates. The spaces between these ridges 

 and those of the basals are marked with a few small nodes, which below the 

 basi-radial suture are arranged in transverse lines. The upper lateral angles 

 of the radials are not truncated, and the facets are shallow. Anal plate 

 similar in form to the radials, but narrower and angular at the top. Costals 

 two, short, and closely united. Distichals three; the length of the two 

 lower plates together about equal to that of the third. Arms four to the 

 ray, subcylindrical, very little tapering ; composed of two rows of rather 

 large interlocking pieces. Pinnules long. Structure of the disk not known. 

 Column round and of moderate thickness ; the joints very even and short 

 near the calyx, but growing longer downward, and the nodal joints project- 

 ing above the internodals. 



Horison and Locality. — Upper Burlington limestone ; Burlington, Iowa. 



Tyipe in the University Museum at Ann Arbor, Michigan. 



Dichocriniis ovatus 0. and Shum. 

 Plate LXXri. Fig. 7, and Plate LXXVII. Figs. 8a, b. 



1S53. Owen and Shtjiiaiid ; V. S. Geol. Rep. Wise, Iowa and Minn., Part II., p. 590, Plate &J, Figs. 



9a, i, c. 

 18SI. W. and Sf. ; Revision Palfeocr., Part II., p. 84. 



Form of calyx ovoid, higher than wide, widest across the middle of the 

 radials; the edges of the plates slightly beveled, and the suture lines well 

 defined ; plates strong. The basals form a rounded, somewhat conical cup, 

 which at its lower end is truncated and slightly excavated. The truncated 

 part is completely filled by the upper face of the column, and there is around 

 its edge a ring of well defined spinous nodes. The sides of the cup are 



