592 



GEOLOGICAL SURVEY OF IOWA. 



Summit composed of numerous small plates and a sub- 

 central proboscis. Surface granulose. 



This species is remarkably distinct from any described, in the character of base 

 and walls of calyx, and still more in the spreading crown and laterally projecting 

 supraradial plates. 



Fig. 3 a. Anterior side of specimen. Fig. 3 b. Anal side. 



The accompanying diagram 

 illustrates the form and arrange- 

 ment of the plates of the body 

 and rays to the fourth subdivi- 

 sion. This may be regarded as a 

 type of those species with broad 

 spreading summits and nume- 

 rous arms. The number of se- 

 condary plates in the rays and 

 the number of arms are fully 

 equal to those of the large species 

 of the Megistocrinus of OWEN, 

 and the arrangement is the same 

 as in that fossil. 



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

 lington, Iowa. 



Actinocrinus aeqnalis ( n. s.). 



PLATE XI. FIG. 4 a, b. 



CALYX somewhat urnshaped, abruptly spreading from the 

 summit of the radials : dome depressed conical, terminating 

 in a strong central proboscis : arms situated about midway 

 between the base of calyx and the base of proboscis : base 

 symmetrically hexagonal, the centre abruptly concave for 

 the reception of the column ; the lower margins truncate, 

 with a broad groove at the suture lines. First radial plates 

 wider than long, subangularly tuberculiform. Second radial 

 plates quadrangular, very small. Third radials pentagonal, 

 the upper sloping sides supporting each a series of two or 

 three supraradial plates; the upper ones pentagonal, and 



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