684 



GEOLOGICAL SURVEY OF IOWA. 



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

 Illinois. 



Zeacrinus magnoliseformis. 



Zeacrinus magnoli&formis : TROOST in MS. of Monograph of the Crinoideae, etc. ; and in 

 Catalogue, Proceedings of American Association for Advancement of Science, 1849, p. 61. 



BODY and arms cylindrical when closed, robust : base 

 concave, the cavity deep, involving the basal, subradial, and 

 lower half of the first radial plates. Basal plates small : 

 subradial plates extremely elongated, unequally hexagonal. 

 First radial plates about as wide as long, extremely attenuate 

 below, and terminating in an acute point. Second radials very 

 short, more than twice as wide as long, obtusely wedgeform 

 above, and supporting a pair of arms which bifurcate on the 

 third or fourth plate above, and again dichotomise once or 

 twice in the course of their length. The anterior ray has a 

 single intercalated quadrangular plate, giving three radial 

 plates to that ray. 



Fia. 112. 



a 



The accompanying diagram is from the 

 original specimen of Dr. TROOST, the anal 

 plates and one ray being concealed in the 

 stone. 



Geological position and locality. In the Kaskaskia limestone ( " Pen- 

 tremital limestone" ) : Tennessee. 



GENUS AGASSIZOCROTUS (TROOST). 



" GENERIC CHARACTER. Pelvis composed of five plates, ter- 

 minating at the base in a solid point, without cicatrix for a 

 column. 



