63 



Basals form a pentagonal disc, with a height very little ex- 

 ceeding the thickness of the plates, and being slightly concave 

 on the lower side where the column attaches. The first radials 

 stand nearly upright, and are a little longer than wide. They 

 are broadly convex, the greatest convexity being at the mar- 

 gins of the articulating facets. The articulating facets are 

 semicircular, occupy about half the diameter of the plates, are 

 gently concave and directed upward at an angle of about forty- 

 five degrees. The notch for the ambulacral canal is only faintly 

 indicated on each plate. 



The azygous interradial, as shown by the angle for its re- 

 ception, is much larger than either of the other interradials. 

 The vault is probably high, as indicated by the round cavity 

 and indistinct ambulacral notches, though it is not preserved 

 in our specimens. 



We do not know of any species with which this one might 

 be confounded, and, therefore, think it is unnecessary to draw 

 comparisons. 



Found by C. S. Hodgson, in the Burlington Group, in Adams 

 county, Illinois, and now in the collection of S. A. Miller. 



PLATYCRINUS HODGSONI, n. Sp. 



Plate V, Fig. 8, basal view; Fig. 9, side view, showing the azygous 

 interradial on the left. 



Species large and wonderfully ornamented. Calyx bowl- 

 shaped, pentagonal, very broadly truncated below, sutures 

 beveled, plates flattened. Surface ornamented with numerous 

 pustules along the beveled sutures and irregular rounded nodes 

 over the interior part of the plates. Plates not very thick. 

 Column round. Arms unknown. 



Basals form a large, almost flat, pentagonal disc. It is 

 slightly concave where the column attaches. Column round 

 and radiately lined near the margin. The basal disc and radials 

 are ornamented in the same manner. The first radials are a 

 little longer than wide, and stand nearly upright. They are 

 flattened below the articlating facets. The articulating facets 

 are semicircular, or occupy a little more than the space of 

 half a circle, and a little more than half the diameter of the 

 plates. They are deeply concave and radiately lined for the 

 firm attachment of the second plates. The facets are directed 

 upward at an angle of about forty-five degrees. The notch 

 for the ambulacral canal is only faintly indicated on each plate. 



