39i PROCEEDINGS OF THE ACADEMY OP 



somewhat in length. Third radials larger than the first, considerably wider 

 than long, unequal, and presenting a triangular outline, the under side being 

 longer than either of the others; supporting on their superior sloping sides 

 the first divisions of the arms. Anal piece smaller than the subradials, a little 

 narrower below than above, apparently pentagonal, though the upper side is 

 not distinctly visible in the specimen described ; extending partly above the 

 summit of the first radial plates. 



The arms are large, rounded, apparently simple, after the division on the 

 third radial piece, and composed of a single series of pieces, which are wider 

 than long, and alternately a little longer and shorter on the opposite sides. 



The plates below the second radial series are remarkable for their thickness, 

 and tumid, angular character, though the angles are not acute. On the sub- 

 radials two of these angles or ridges pass from the middle to the base, nearly 

 parallel to each other, and one to each of the first radial pieces above. On the 

 first radials there are two of these angles, both of which pass from above 

 obliquely to the base, where they connect with those on the subradial pieces, 

 giving to each first radial a bilobate appearance, 



Locality and position. Nauvoo, Illinois. Keokuk Limestone of lower car- 

 boniferous series. 



Genus POTERIOCRINUS, Miller. 



Poteriocrinus (Scaphiocrinus) decadacttlus. Body rather small, broad, 

 obconical below the arms, expanding rapidly from the base ; plates somewhat 

 thick, nearly smooth, not convex, and connected by moderately distinct, 

 sutures. Base small, convex, or about half as high as wide, pentagonal in out- 

 line as seen from below, the upper angles of the plates being rather salient. 

 Subradial plates somewhat unequal, a little wider than long, four of them 

 hexagonal, and one on the anal side heptagonal ; the upper sloping sides in all 

 longer than those beneath, which are longer than the lateral margins. First 

 radial plates about twice as long as the smaller of the subradials, four of them 

 pentagonal, and one hexagonal, all wider than long, and wider on the upper 

 horizontally truncate side than either of the others. Second radials about the 

 size of the first, pentagonal, a little wider than high, truncated below, and pro- 

 vided with a salient angle in the middle above ; supporting the arms on their 

 superior sloping sides, which are longer than the lateral margins. 



The first anal plate is large, or equalling some of the subradials in size. It 

 is irregularly hexagonal in form, and rests between the superior sloping side? 

 of two of the subradials, supporting on its right (longest) sloping side an in- 

 ferior edge of one of the first radial pieces, and connecting on the left 

 by a short vertical edge, with another first radial plate. On its upper sides it 

 supports two smaller pieces in the second range, the exact form of which can- 

 not be made out in the specimen examined. 



The arms are long, large, and robust, subcylindrical, rather unequal, and 

 appear to be all simple from their division on the second radial piece. They 

 are entirely composed of a single series of pieces, a few of the first of which 

 are longer than the others, and alternately longer and shorter on opposite 

 sides ; further up they are more regular, and shorter than wide. The 

 column is rather small, or less than the diameter of the largest arms; it is 

 round, and composed of thin, slightly unequal segments near the body. It? 

 central cavity is small, and presents a regular pentapetalous section. 



Height of body from base to the summit of second radials, 0-48 inch ; breadth 

 about 0-47 ; length of arms, apparently not less than 2-50 inches ; breadth of 

 do. from 0-11 inch to 0-16 inch. 



Locality and position. Appanoose, Hancock county, Illinois. Keokuk Lime- 

 stone, of snbcarboniferous series. 



Poteriocrinus Swallovi. Body of medium size, obconical, or tapering regu- 

 larly from above to its connection with the column ; composed of smooth, 



[Sept. 



