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FOSSILS OF THE KEOKUK GROUP. 407 



-ion. three secondary radials of nearly the same sixes 

 and forms as the primary radials; of these the last one of 

 each series is an axillary piece, and bears smaller tertiary 

 radials, a portion of which, in those having seven or more 

 pieces, being free, and the last one in each series bearing 

 two subdivisions, one of which is a simple free arm smaller 

 than the other division, which latter divides again on the 

 iifth. seventh or eighth piece, the smaller inner division 

 being a simple arm, while the other bifurcates so as to form 

 at least two arms farther up, thus making, as far as can be 

 seen in the specimen, eight arms to each of the two main 

 divisions of each ray, or eighty to the entire series. Arms 

 all comparatively short, flat, or very nearly so, on the dor- 

 sal side, and in contact laterally all around, when folded 

 upward. 



Interradial arms lance-ovate, or elongate sub-rhombic, 

 and nearly or quite even with the radial series on each side ; 

 occupied each by from twenty-five to thirty pieces, com- 

 mencing below with one hexagonal piece in the first range, 

 over which are two in the second range, three in the third, 

 three or four in the fourth, fifth, sixth and seventh, while 

 the remaining smaller pieces are irregularly arranged in 

 the gradually narrowing space above. Anal area wider 

 below than the interradial areas, and like them nearly or 

 quite even with the radial series on each side ; occupied by 

 about thirty pieces, arranged with two in the first range, 

 and four in two or three of those above, while the narrow- 

 in ji space over the latter is occupied with irregularly dis- 

 1 Hi>ed smaller pie< 



Interaxillary areas with eleven to about thirteen small 

 pieces each, arranged in two series above the first one; in- 

 teraxillary spaces, or the second order, each occupied by 

 three or four pieces in direct succession. 



Patelliform pieees intercalated between the different 

 ueces of the radial scries, well developed all the way up 

 into the arms. 



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