176 PALAEONTOLOGY OF ILLINOIS. 



Vault subconical, pentalobate; summit plates prominent, the 

 central one sharply tuberculous, showing a tendency to become 

 spiniferous. 



Column round, composed of long joints with rounded edges, 

 which alternate near the calyx with very short and narrow 

 pieces. 



Geological position, etc.: The same as the preceding species. 



Our own collection. 



Remarks : It is possible that this Kinderhook form is specifi- 

 cally identical with Dorycrinus (Actinocrinus) helice Hall from 

 the Waverly group of Ohio. 



DORYCRINUS RADIATUS (nov. sp.) W. & Sp. 



PI. XVII, Fig. 5. A specimen with arms from the posterior side. 

 PL XVII, Fig. 5a. The same from the 'anterior side. 



Dorycrinus radiatus somewhat resembles D. immaturus, but 

 differs from that species in the arm formula, and in being the 

 only species of this genus which has radiating ridges along the 

 plates. From every first radial two low, rounded ridges pass 

 to the basals, two to the adjoining radials and anal plate, and 

 one to each first interradial. The interradials have nine ridges 

 two connecting with the first radials ; two with the second, and 

 two with the third radials, while the remaining three which are 

 smaller pass into the three interradials of the second range. 

 The ridges are well defined next to the margins of the plates, 

 but become indistinct, or disappear entirely, in the middle. 

 Color rather lighter than in the last species. 



Dorsal side of the calyx subconical, wider than, high, truncate 

 at the base, a little convex along the sides. Basal cup short, 

 broad, with projecting lips, extending in width considerably be- 

 yond the limits of the column, and slightly beyond the lateral 

 walls of the calyx. 



First radials somewhat lower than those of the preceding 

 species, the second and third radials proportionately a little 

 higher. The secondary radials vary among the rays, consisting 

 in the anterior ray, which has but two arms, of two com- 

 paratively large, transverse pieces, which are succeeded by 

 free, cuneiform plates, interlocking, and gradually turning into 

 two series of transversely arranged arm pieces. The other four 



