552 



GEOLOGICAL SURVEY OF IOWA. 



ARMS double from their origin on the second radial plate, 

 rounded below and subangular above, in some parts having 

 small nodes upon the back ; each arm consisting of a single 

 series of joints which are wider than long, with nearly pa- 

 rallel faces in the lower part, while towards the summit they 

 become distinctly wedgeform ; the thicker side of each plate, 

 near its upper edge, showing the point of attachment for 

 tentacula. 



In the Graphiocrinus figured by DE KONINCK, the plates are proportionally longer, 

 and have the articulating faces parallel quite to the summit, or as far as represented. 



Fig. 10. Anal side of specimen described. 



Geological formation and locality. In the Burlington limestone : Bur- 

 lington, Iowa. 



have thus each a part of one of the lateral edges sloping. The second radials are cunei- 

 form or pentagonal, each giving origin to a pair of arms which are not bifurcating, but 

 composed of articulations with the articulating surfaces parallel to each other, and fur- 

 nished interiorly with fine and short pinnules". 



Recherches sur les Crinoides du Terrain carbonifere de la Belgique, p. 115. 



The following diagram illustrates the structure of the typical form of the genus 

 as given by the authors cited above. 



FIG. 71. 



GENERIC FORMULA. 



Basal plates, 5. 

 Radial plates, 2X5. 

 Anal plate, 1. 

 Interradial, 0. 

 Arms 10, not bifurcated. 



