13 



the tenth, plate, makmg eight arms to each of these rays. The 

 other rays are partially embedded in the matrix, minute projec- 

 tions are visible, with a good glass, on the outer side of the arm 

 plates, that give a roughened aspect to the whole specimen, and lias 

 suggested the specific name, and will also serve to distinguish it 

 from nearly related species. 



Anal plates so closely anchylosed that their forms cannot be clearly 

 determined, but the first one rests between two of the subradials, 

 and is succeeded by a double series of smaller plates that apparently 

 go to form the base of the ventral tube. Traces of coarse striae, or 

 rows of granules, extending across the brachial plates, as well as the 

 radials, can be seen with a good glass. 



Column round, composed of rather even joints, with numerous 

 delicate cirrhi attached to it at short intervals. 



Position and locality : Upper part of the geodiferous shales of 

 the Keokuk group ; one mile below Keokuk. 



No. 234 of Mr. L. A. Cox's collection. 



POTERIOCEINUS ARACHNyl5F0RMIS. N. SP. 



Body small, obconical, length and breadth about equal, gradually 

 swelling from the base to the summit of the radial series. Basals 

 projecting more than half their length beyond the column, and 

 forming by themselves a low, pentagonal cup. Subradials compar- 

 atively large, three hexagonal, and two heptagonal. Radials smaller 

 than the subradials, the articulating scar semi-circular, and occupy- 

 ing only about half the width of the plate, with a projecting rim 

 around its outer margin. 



Only one anal plate is preserved in the specimen under descrip- 

 tion, which is about half as large as the largest of the subradials 

 between which it rests, and it extends up to the summit of the right 

 posterior radial. The left posterior subradial is truncated at the 

 summit for the support of the second anal, which is not preserved. 



Only one of the rays is partially preserved. In this there are five 

 brachials, the last one of which is an axillary plate, and supports 

 the first divisions of the ray, one of which divides again on the third 

 plate, beyond which the arms are not preserved. The arms are 

 composed of long, slender, rounded joints, generally twice as long as 

 wide. 



Column unknown. 



Position and locality : Keokuk limestone, Warsaw, 111. 



Illinois State collection. 



POTERIOCRINUS NAUVOOENSIS. N. SP. 



Body small, cup-shaped, the plates being displaced somewhat by 

 crushing, prevents a complete diagnosis. 



Basals small, and hidden by the first columnar joints. Subradials 

 as high or higher than wide, and sharply angular above. Eadials 



