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 ob- 

 tained 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 BURKETI N. SP. 



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 divisions 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- 

 radials, and this is succeeded by a double series of minute plates 

 that form the lower extremity of the ventral tube. This organ is 

 composed of minute plates, is balloon shaped, and shows a small 

 opening about two-thirds the distance from the base to the summit. 

 Column at the top composed of round, nearly uniform plates, but a 

 short distance below thicker joints are intercalated at irregular inter- 

 vals. It decreases in diameter nearly one half in a distance of two 

 inches from the top, and has delicate cyrrhi attached on either side 

 at irregular intervals. 



The depressions at the angles of the body plates, gives to the ex- 

 terior of the cup-shaped body a somewhat rough appearance. 



This species is named m honor of Mr, N. K. Burket, of Keokuk, 

 Iowa, who discovered the interesting locality at Hamilton, where 

 this and several other new forms have been obtained. 



Position and locality : Top of the Keokuk limestone, Hamilton, 

 Illinois. 



. Nos. 260 and 402 of Mr. L. A. Cox's collection. 



