PLATE 49. 

 Oligoporus blairi Miller and Gurley. Page 351. 



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Figs. 1-3. Keokuk Group, Lower Carboniferous, Boonville, Missouri. Univ. of Chicago Coll., 6,470, cotypes. Natural 

 size. Melon-like ribs moderately developed, ambulacral plates demi-, occluded and scattered isolated. 



Fig. 1. Interambulcra A, C, and E each with seven columns of plates. Drawing of this specimen, Plate 47, fig. 7. 



Fig. 2. In interambulacrum A there are six columns of plates, the initial pentagon of column 6 lying on the right of the 

 center just below the mid-zone. In interambulacrum C there are seven columns of plates. The initial pentagon 

 of column 5 is in the middle line near the ventral border; the initial pentagon of column 6 lies three rows above on 

 the left of the center, and the initial pentagon of column 7 lies again three rows above in the center and just above 

 the mid-zone. 



Fig. 3. In interambulacrum A there are six columns of plates, the initial pentagon of column 6 with a heptagon on its 

 right ventral border lying on the left of the center and below the mid-zone. In interambulacrum C the initial penta- 

 gon of column 6 lies on the left of the center and appears somewhat earlier than in area A. The initial pentagon 

 of column 7 with a heptagon on its right ventral border appears just above the mid-zone. Above this zone on the 

 right, the plates are displaced and confused. 



Oligoporus danae (Meek and Worthen). Page 356. 



Fig. 4. Keokuk Group, Lower Carboniferous, Adams County, Illinois. Mus. Comp. Zool. Coll., 3,142 (from R. T. J. 

 Coll.). Natural size. Ambulacra with demi-, occluded, and scattered isolated plates. Interambulacra with nine 

 columns of plates in each area, the ninth appearing at the mid-zone. Drawing, Plate 50, fig. 1. 



Fig. 5. Same specimen, reverse side. Natural size. Both interambulacra with nine columns of plates. Drawings, Plate 

 50, figs. 2-6. 



