NATURAL SCIENCES OF PHILADELPHIA. 157 



tentacle. Above the bifurcation on the tenth piece, the divisions are very- 

 long, slender, somewhat angular on the outer side, and still composed of a 

 single series of wedge-shaped pieces, each one of which is strongly protuberant 

 laterally, for the reception of a tentacle at its larger end, the protuberances 

 and the sinuosities between giving the divisions of the arms a zigzag appear- 

 ance, somewhat like those of Platycrinus nodobrachiatus, Hall.* 



Surface apparently smooth, or only finely granulose. Suture not impressed 

 between the plates of the body, but somewhat gaping between the first and 

 second radials. 



Height of body to top of first radials, 0-41 inch ; breadth, 0-60 inch. Length 

 of arms to first bifurcation, 0-70 inch; entire length nearly 3 inches. 



This species seems to be related to several of those described by Prof. Hall 

 from the same locality and position, but on comparison will be found not to 

 agree in all its characters with the description of any of them. From his S. 

 spinobrachiatus it evidently differs in not having the plates of the body convex, 

 nor the sutures indented at their angles, as well as in not having the arms 

 subspinous, and the whole body is less broadly cup-shaped. 



From S. Whitei, Hall, it differs in not having the " surface of cup marked by 

 deeply impressed pits " at the junction of the sides of the subradials, and 

 between the first radial pieces: and from S. Halli, Hall, it differs in not having 

 the arms simple after the first division on the second primary radial, as well 

 as in some of the details of their divisions. 



Locality and position. Burlington, Iowa. Burlington Limestone of Snb- 

 carboniferous series. 



POTERIOCEINUS (SCAPHIOCRINUS) BaYENSIS, M. & W. 



Body of medium size, rather depressed obconic below the top of the first 

 radials. Base about twice as wide as high, expanding directly from the head 

 of the column on a line with the subradial and first radial pieces. Basal pieces 

 moderately developed, wider than long, pentagonal, and showing the whole 

 surface of each in a side view. Subradials about three times as large as the 

 basal, somewhat wider than long, three hexagonal, and two on the anal side 

 apparently heptagonal, the angle on the middle of the under side of all being 

 very obtuse. First radial pieces wider and a little shorter than the subra- 

 dials, all pentagonal, apparently transversely truncated their entire breadth 

 above. Second radials of nearly the same size as the first, and like them pen- 

 tagonal, but having the middle angle above and more salient, while the two 

 superior sloping sides each supports an arm, thus giving origin to two arms to 

 each ray, or ten to the entire series ; all of which are nearly in contact all 

 around below, excepting on the anal side. 



First anal piece smaller than the subradials, hexagonal in form, and resting 

 between the upper sloping sides of two of the subradials, with its upper right 

 edge supporting one side of one of the first radials, and its left connecting 

 apparently with a second anal piece, the form of which cannot be made out in 

 our specimen. In the third range, one piece evidently rested upon the upper 

 truncated edge of the first anal piece, but its form and connection with the 

 other pieces on the left have not been determined. 



Arms long, and, as far as can be determined, apparently simple after the first 

 division of each ray on the second radial piece ; each composed of a single 

 series of wedge-shaped pieces, alternately longer and shorter on opposite sides, 

 but not protuberant on either side ; those near the lower part about as long on 

 the longer side as their breadth. Tentacles numerous, rather stout, and com- 

 posed of joints three or four times as long as wide, and not swollen or dilated 

 at the ends. 



Column of moderate thickness near the base, where it is round and com- 



*Iowa Report, p. 542. 



1865.] 11 



