ECHINODERMATA—CRINOIDEA. 509 



composed of cuneate joints. Column round or somewhat five- 

 sided. Devonic-Mississippic. 

 35. P. agnatus Miller. Mississippic. 



Calyx cup-shaped, wider than high; each ray with a single 

 brachial. Surface smooth. Arms 16, several bifurcating. 



Keokuk of Missouri. 

 ^6. P. amaenus Miller. Mississippic. 



Calyx as in P. agnatus, but smaller and surface granular. Some 

 rays with a simple brachial and some with double. Arms 16, flat- 

 tened externally and fitting closely together. 



Keokuk of Indiana. 



XVI. SCAPHIOCRINUS Hall. 



Dorsal cup low, saucer-shaped. Plates as in Poteriocrinus, but 

 articular facets of the R horizontal and completely occupied by the 

 lower faces of the first brachials. Arms 

 long, uniserial and branching, composed of 

 wedge-shaped plates. Mississippic-Car- 

 bonic. 

 :i,y. S. swallovi (Meek and Worthen). 



Mississippic. 



Calyx below the arms tapering regularly 

 down to the column, composed of smooth 

 plates. Arms long and rounded, bifur- 

 cating, uniserial. 



Burlington-Keokuk of Iowa. ^^^- '^^^' ^'TJ^'ln 



^ uniiUs^XYz' (After Meek 



38. S. UnicUS Hall. (Fig. 1823.) and Worthen. ) 



Mississippic. 

 Distinguished by the single undivided arm of the anterior ray. 

 Keokuk of Indiana. 



39. S. crineus Hall. (Fig. 1824, a,.h.) Mississippic. 

 Plates of arms strongly wedge-shaped. Surface smooth or 



finely granulose. 

 Waver ly of Ohio. 



40. S. subcarinatus Hall. (Fig. 1824, c, d.) Mississippic. 

 Small, with slender arms. Calyx plates angular in the middle. 



Surface granulose. 

 Waverly of Ohio. 



