5G2 GEOLOGICAL SURVEY OF IOWA. 



GENUS ACTINOCRINUS : 

 Submenus? Agaricocrinns (TROOST). 



FIG. 77. 



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GENERIC FORMULA. 



Basal plates, 3. 



Radial plates, 3X5 = 15. 



Anal plates, 4 to 7 or more. 



Interradial plates. 



Brachial plates, 2 or more. 



Arms dividing on the last radial, and 

 composed above the brachial plates 

 of a series of short, wide plates. 



Agaricocriiius bullatus ( n. s.). 



PLATE IX. FIG. 11 a, b. 



GENERAL form convex hemispheric above, and deeply con- 

 cave beneath : basal plates hidden by the column. First 

 radial plates five, hexagonal, about as long as wide, abruptly 

 bent upwards on their inner margins, and closely embracing 

 the column. Second radial plates quadrangular, nearly twice 

 as wide as long. Third radial plates pentagonal, the length 

 about two-thirds the width, the two upper oblique sides 

 supporting each brachial plate, and these two supporting 

 four other arm-plates. First interradial plate elongated, 

 resting below on the upper oblique sides of the adjacent first 

 radial plates, reaching nearly to the summit of the brachial 

 plates, and supporting upon its short upper side two narrow 

 interradial plates which rest between this and the adjacent 



