68 OWEN AND SHUMARD'S FOSSIL CRINOIDEA. 



massive plates, tumid in the centre, surround the basal plate, five are hexagonal, and 

 one is irregular and heptagonal. The second series consists of twelve pieces, five are 

 quadrangular, short, (their height being to their breadth as one to two,) slightly 

 arcuated on their edges, and rest on the upper edges of the hexagonal plates of the 

 first series; four are nine-angled, one being situated between each pair of 

 quadrangular plates, and their inferior salient angles are inserted in the retreating 

 angles formed by the union of the hexagonal plates of the first series ; two are 

 irregularly heptagonal, and one hexagonal, these repose on the upper edges of the 

 heptagonal plate of the first series. Each of the above mentioned quadrangular 

 plates is surmounted by a widened pentagonal plate, which again supports on its 

 oblique upper edges two short irregular pieces, sub-hexagonal or pentagonal, with 

 their superior margins slightly concave to accommodate the arm bearing plates, 

 which are small and somewhat horse-shoe shaped. All the pieces which we have 

 mentioned above the basal plate are elevated in their centres, which gives to the 

 surface of the visceral cup an uneven appearance. 



The coronal integument is made up of numerous polygonal plates. The central 

 one is a little larger than the rest, and is garnished with a spinous process which is 

 often produced to a half of an inch in length ; the others are usually tumid in their 

 centres and wrinkled ; in some specimens, however, they are furnished with 

 projecting tubercles, some of which are flattened and divided into two or more points. 



Mouth sub-central, protrusive but not proboscidiform. It is situated near the inner 

 extremity of a prominent ridge composed of small irregularly shaped plates. This 

 ridge commences at the central spinous plate, and terminates at the outer border of 

 the cup between two of the arms. 



Arms twelve, bifurcations unknown. Column undiscovered. 



It occurs rather abundantly in the sub-carboniferous limestone at Burlington and 

 Augusta, Iowa. 



ACTINOCRINUS EVANSII. (NcW Sp.) 



Fig. 3, a, h. 



The body of this fine species has the form of an inverted truncated cone, with a 

 moderately rounded base. 



Basal plate large, somewhat massive, hexagonal, tripartite, divisions equal, 

 flattened, slightly concave near the margin, and moderately convex towards the 

 centre. The impression for the attachment of the column is large, occupying nearly 

 one half the diameter of the plate, slightly excavated and striated on the margin, 

 perforation large, obscurely pentagonal. 



