ECHINODERMATA—BLASTOIDEA. 



487 



Fig. 1800. Cadaster pyramidatus^ sum- 

 mit view, X 2^, and lateral view, X 2. 

 (After Etheridge and Carpenter.) 



due to the alternation of the radiating oral ridges with the ambu- 

 lacra. Greatest circumference always nearer the summit end of 

 the calyx. Basal plates forming a deep conical or triangular cup. 

 Radial plates large, never 

 deeply excavated by the si- 

 nuses. Deltoids wholly con- 

 fined to the summit, four of 

 them irregularly triangular and 

 bearing prominent ridges and 

 the fifth more triangular than 

 the others, without a ridge 

 and pierced by the anus. Am- 

 bulacra confined to the upper 

 face and petaloid or narrow and linear ; lancet plate usually deeply 

 excavated for the side plates. Hydrospires suspended vertically 

 in the calyx, two in each interradius except the azygous one, and 

 opening externally by a variable number of slits, partly in the 

 truncated upper surfaces of the radials and partly in the deltoids 

 and nearly parallel to the ambulacra. Siluric-Mississippic. 



2(y. C. pyramidatus Shumard. (Fig. 1800.) Devonic. 



Radial plates bearing flattened marginal bands. 

 Onondaga of New York, Kentucky and Ohio. 



27. C. alternatus Lyon. Devonic. 



Differs from C. pyramidatus in its concave summit and in the 

 absence of the flattened marginal bands of the radials. 



Onondaga-Hamilton of Kentucky. 



,^^^Jv 



Fig. 1 80 1. Oropho- 

 crinus stelli/ormis, side Fig. l8o2. Orophocrinus stelliformis, enlarged ventral 



and stem view. (After view, a, end of vault ; am, ambulacral furrows ; an, anal 



Meek and Worthen, 111. aperture; .y, spiracles; v, oral vault. (After Meek and 



Geol. , V. ) Worthen, 111 . Geol. , V. ) 



