ECHINODERMATA—CYSTOIDEA. 465 



II. C. ornatus Say. (Figs. 1771-1773.) Siluric. 



Greatest diameter of calyx usually below the middle. Summit 

 slightly convex, with arms sometimes several inches long. Upper 

 margins of radial and interradial plates indented for the arm plates. 

 Pores represented on the exterior of the plates by single or double 



Fig. 1772. Caryocrinus ornatus. (Af- Fig. 1773. Caryocrinus oj-natus, basal 

 terHall.) view. (After Hall.) 



rows of tubercles radiating from the center of the plates to their 

 angles; between these are numerous rows of smaller tubercles 

 parallel to the sides of the plates. (Type of genus.) 

 Rochester shale of New York and Ontario. 



12. C. bulbulus Miller and Gurley. Siluric. 

 Smaller than C. ornatus and with smooth surface. Calyx hex- 

 agonal in the middle by reason of the central protuberances on 

 each of the six plates of the second row. 



Niagaran of Tennessee. 



VIII. Pleurocystites Billings. 

 Calyx compressed laterally; convex side composed of large 

 plates arranged in cycles; flattened side covered with very minute 

 plates. Arms two. Pectinated rhombs three, borne on the convex 

 side. Anal opening at side of base. Column round, short, tapering 

 distally to a point. Ordovicic. 



13. P. squamosus Billings. (Fig. 1774.) Ordovicic. 

 Large plates smooth ; rhombs small ; the longer axes of the 



upper two are transverse to the length of the calyx. (Type of 

 genus.) 



Trenton of Ottawa. 



