682 GEOLOGICAL SURVEY OF IOWA. 



This species is more depressed and shorter in the body and rays than any other 

 of this genus known to me. It presents the characters of Zeacrinus in its small basal 

 plates, long subradials and short second radial plates; 

 while the base is scarcely depressed and the arms have 

 more the expression of Scaphiocrinus in their branch- 

 ing, while the plates are of the form corresponding to 

 Ztacrinus. The form is one showing the intimate rela- 

 tions of the two genera, and may with almost equal 

 propriety be referred to either. The extremities of the 

 two types may be seen by comparing the generic illu- 

 stration on page 550 with the following one on page 

 684. 



Fig. 4. The anterior side of the specimen, which. has the arms of this ray broken off 

 above the first bifurcation. 



Geological position and locality. In the Kaskaskia limestone : Chester, 

 Illinois. 



Zeacrinus maniforiuis. 



PLATE XXV. FIG. 8. 



Poteriocrinus maniformis : YANDELL and SHUMARB, Contributions to he Geology of 



Kentucky, 1847, pa. 24, pi. 1, f. 2. 

 Cyathocrinus maniformis : Y. and S., Catalogue, etc. 



Cyathocrinus gracilis : TROOST, Catalogue, 1849. 



BODY subcylindrical, concave at the base, rounded and 

 gibbous above, the concavity involving the lower half of the 

 subradial plates, depressed subconical above when the arms 

 are closed. Basal plates hidden by the column : subradial plates 

 longer than wide, the lower half abruptly bent inwards to 

 form the exterior cavity ( the upper half of the plates only 

 showing in the figure). First radial plates wider than long, 

 pentagonal. Second radials shorter than the first, obtusely 

 wedgeform above, and supporting on the sloping sides a pair 

 of arms, which are composed of a series of short quadrangu- 

 lar plates, alternately longer and shorter on the same side 

 of the arm, the longer faces supporting the tentacula. Arms 

 simple throughout their entire length. 



COLUMN, near the base of the body, composed of alternating 

 thicker and thinner joints. 



