588 GEOLOGICAL SURVEY OF IOWA. 



anal series three, with two small irregular plates above, and 

 beyond this sometimes a narrow elongate plate lying between 

 the arm-bases. 



AKMS composed of a double series of short slightly inter- 

 locking plates, which, when perfect, are marked by three or 

 four distinct nodes with the intermediate spaces granuliferous, 

 with tentacles from the centre of the inner edge. 



SURFACE beautifully granuliferous. 



This neat and pretty species has a symmetrical urnshaped calyx, with the arms 

 all similar, equidistant from each other, and closely arranged. The only irregularity 

 in the arms is the additional one from each postero-lateral ray. 



Fig. 1. Posterior side of specimen, showing arrangement of radial and anal plates. 

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

 lington, Iowa. 



Actinocrinus turbinatns, var. elegans. 



PLATE XI. FIG. 5. 



This specimen has the same general form as the preceding, symmetrical calyx and 

 hemispheric summit : the radial plates and arms are of the same form and number; 

 the first interradial plate differs in being nine-sided, and supporting upon its upper 

 edge a single small pentagonal plate, and above this another small hexagonal plate, 

 instead of the two and one as in the other. The second series of anal plates are pro- 

 portionally larger than in the preceding form; and the third series consists of three 

 irregular plates, and two narrow ones above between the bases of the arms. The arms 

 are arranged in a precisely similar manner, being a little stronger at their bases : 

 the basal plates are squarely truncate below, and indented at the sutures; while 

 those of the other are rounded, and not thus indented. 



FIG. 87. 



D number and arrangement of the plates of the 



The accompanying diagram illustrates the 

 mber and arrangement o 

 ^nr\<C\\ y*~JLJ[) body and bases of the arms. 



