270 PALEONTOLOGY OF ILLINOIS. 



served. The arms are stout, and composed of rounded, short, nearly 

 parallel plates, that give off delicate pinnules from their inner mar- 

 gins. The uppper part of the ventral tube is exposed by the partial 

 removal of the arms, showing that this organ was trumpet-shaped, 

 and crowned with heavy hexagonal plates, produced at the center 

 into rather sharp nodes, while below the plates are thinner, and 

 crossed by about three sharp ridges, that are most prominent in the 

 center of the plate. Similar ridges are also visible on the margins 

 of some of the summit plates. Anal plates unknown. Column 

 round and rather stout, composed of thin, even plates. Length of 

 body and arms 5f inches, breadth at the summit of the ventral 

 tube 2f inches, length of column 7f inches. 



This magnificent specimen of Poteriocrinus, the finest ever obtained 

 from the Keokuk limestone, I take pleasure in dedicating to Mr. 

 L. A. Cox, of Keokuk, Iowa, to whom it belongs, in recognition of 

 his zeal and untiring industry in collecting the crinoids and fishes 

 of that vicinity. 



Position and locality : Upper part of the Keokuk limestone, Ham- 

 ilton, 111. 



Mr. L. A. Cox's collection. 



POTERIOCRINUS BTJRKETI, Worthen. 



PI. XXVIII. Fig. 8. 



Poteriocrinus Burketi, WOETHEN, February, 1882. 

 Bulletin No. 1, of the Illinois State Museum of Natural History, p. 5. 



Body small, cup-shaped below the summit of the first radial 

 plates. Basals small and concealed by the first joints of the column. 

 Subradial plates slightly protuberant from the depression of their 

 upper angles, curving below into the basal concavity. 



Eadials pentagonal, about once and a half as wide as long. Bra- 

 chials -two to each ray, the first quadrangular, and the second the 

 same form as the radials, and supporting on their upper, sloping 

 sides the first division of the arms. The arms after the first divis- 

 ion on the second brachial plate, divide again on the sixth to the 

 ninth plate, beyond which they continue simple to their extremities, 

 making four arms to each ray. Arms composed of slightly wedge- 

 formed plates, about as long as wide below the last bifurcation, but 

 proportionately longer and more zigzag in their arrangement above, 

 giving off strong pinnules alternately from their longest sides. Anal 

 plates small, the first one apparently resting between two of the sub- 



