INVERTEBKATES. 279 



a part of the basal concavity, and the upper angles depressed to 

 correspond with similar depressions in the lower margins of the 

 radial plates. 



Eadials short, about as wide as long, pentagonal, depressed at 

 their lower angles, with a gaping suture between them and the suc- 

 ceeding brachials. 



Brachials two, the first quadrangular, the second sharply angu- 

 lar above, and but little narrower than the radial series. A slight 

 angular prominence extends lengthwise across the brachial plates, 

 and the same may be seen on the lower portion of the arms under 

 a good glass. 



Arms on the anterior ray, after the first division on the second 

 brachial, divide again on the fourth and sixth plate, and both the 

 outer divisions again on the eighth plate, while the inner one ap- 

 pears to be simple after the second division, thus giving six arms 

 to this ray. The antero-lateral rays appear to divide once more, 

 giving eight arms to those rays. 



Arm pieces rounded, moderately wedge-shaped, and diminish 

 rather rapidly in width toward their extremities. Delicate pinnules 

 are given off from their longest sides. Anal plates and column un- 

 known. 



The depressions at the angles of the body plates, give a rugged 

 appearance to the body of this species, and will serve to distin- 

 guish it from the other forms with which it is associated. 



Position and locality: Upper part of the geodiferous shales of the 

 Keokuk group, one mile below Keokuk. 



No. 191, Mr. L. A. Cox's collection. 



POTEBIOCRINUS BRUERIUS, Worthen. 



PL XXVII, Fig. 4. 



Poteriocrinus brmrius, WORTHEN, February, 1882. 

 Bulletin No. 1, of the Illinois State Museum of Natural History, p. 12. 



Body of medium size, cup-shaped, base depressed; the basal 

 plates small, not extending beyond the columnar facet. Subradials 

 prominent in the center and depressed at the angles, three 'hexa- 

 gonal and two on the posterior side rather larger than the others, 

 and heptagonal. 



