564 GEOLOGICAL SURVEY OF IOWA. 



Fio.78. 



The accompanying figure illustrates the structure of the 

 base, and affords means of comparison with A. tuberosus. It 

 will be observed that in one of the antero-lateral rays there 

 are but two radial plates, which is probably an accidental 

 feature, 

 db T 



P 



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

 lington, Iowa ; Quincy, Illinois. 



Agaricocrimis stellatus ( n. s.). 



THIS is smaller than the preceding species, the base less 

 concave, and the whole body more depressed. The basal 

 plates extend beyond the column for more than half the 

 width of the latter. The first radial plates are shorter ; the 

 second radial longer, and the third less gibbous than in A. 

 bulletins ; while the interradial plates are much broader, and 

 the second series much better developed, owing to the greater 

 space between the arms. The second plate above the base of 

 each arm is tuberculous, and also the central plate of the 

 summit. Arms originating in pairs on the second brachial 

 plate ; each arm consisting of a double series of plates, 

 which are twice as wide as long, obtusely wedgeform at their 

 interlocking edges, and tentaculate from their upper outer 

 margins. 



This species corresponds to another species in the Keokuk limestone; while the 

 preceding corresponds to Agaricocrinus tuberosus of the same limestone. 



The accompanying diagram illustrates the form, proportions 

 arrangement of the plates of the lower part of the body and 

 bases of the arms. 



Geological formation and locality. In the Burlington limestone : Quincy, 

 Illinois. 



