NATURAL SCIENCES OF PHILADELPHIA. 141 



piece, which extends nearly half its length above the first radial on its right. 

 The arms above the first division on the second radial plates are strong, angu- 

 lar on the outer side, and (excepting in the anterior ray) bifurcate again on 

 the sixth or eighth plate, beyond which they are simple, as far as they can be 

 traced in the specimen under description. They are each composed of a single 

 series of pieces, which are as long as wide, or somewhat longer, a little wedge- 

 shaped, and alternately prominent or subnodose on opposite sides, so as to 

 give the arms a somewhat zigzag appearance. The surface is finely granu- 

 lose ; and while the sutures are scarcely visible between the body plates, 

 those between the first and second radials are distinctly gaping. 



Locality and position. Burlington, Iowa. Burlington Limestone. Mr. 

 Charles Wachsmuth's collection. 



Poteriocrinus (Scaphiockinus) Wachsmuthi. Body small, inversely bell- 

 shaped below the summit of the first radial plates, wider than high. Base 

 small, scarcely visible in a side view, and extending a little beyond the sum- 

 mit of the column, which is round and composed of rather thin segments near 

 the body. Subradial plates as wide as high, convex, four hexagonal and one 

 heptagonal. First radial plates from one-third to one-half larger than the sub- 

 radials, wider than long, truncated above and pentagonal in form, the upper 

 side being longer than the others. Second radial pieces somewhat larger than 

 the first, distinctly constricted around the middle, about as long as wide, and 

 pentagonal in outline, the upper superior angle being rather acute. First anal 

 plate larger than the subradials, hexagonal in form, resting upon the trun- 

 cated upper side of one of the subradial pieces, and projecting nearly half its 

 length above the first radial plates on each side of it. The arms, after the 

 division on the second radial pieces, appear to be simple, very long, and gra- 

 dually tapering. They are each composed of a single series of joints, all of 

 which are longer than wide, somewhat constricted around the middle, and 

 alternately longer and shorter on opposite sides, the upper extremity of the 

 longer side of each projecting out for the reception of the tentacles, so as to 

 give the arms a zigzag appearance. The tentacles are strong and composed of 

 joints which are two or three times as long as wide, and distinctly grooved on 

 the inner side. 



The surface is granulose, and the sutures well defined ; while at each cor- 

 ner of the subradial plates there is a deep round pit or depression. This spe- 

 cies seems to be related to S. spino-brachiatus of Hall, but differs in the form 

 of its body, and in having longer arm pieces, which are also without spines. 

 It has remarkably long arms, and a neat symmetrical bell-shaped body below 

 the first radials. 



Locality and position. Burlington, Iowa. Burlington Limestone. Collec- 

 tion of Mr. Charles Wachsmuth. 



BLASTOIDEA. 

 Genus PENTREMITES, Say, 1820. 



Pentremites corndtus. Body under medium size, subglobose, broader 

 than high, the widest part being at the middle ; upper and lower extremities 

 truncated. Base deeply concave, and entirely within the concavity of the 

 under side. Radial pieces long, or extending from the base of the body to 

 near the summit ; narrow, somewhat contracted above and below, and divided 

 by the pseudo-ambulacral areas nearly four-fifths their entire length ; all 

 very thick and rising into prominent carinse on each side of the pseudo-ambu- 

 lacral fields. Interradial pieces of moderate size, and each projecting out in 

 the form of a very prominent, compressed horn-like process. Pseudo-ambula- 

 cral areas very narrow, or lance-linear, and deeply implanted between the 

 very prominent, carinated forks of the radial plates. (Summit unknown.) 



Height 0-45 inch, breadth 0'54 inch ; greatest breadth of radial pieces, - 20 

 inch ; breadth of pseudo-ambulacral areas, 0*04 inch. 



This species will be readily distinguished from all the others yet known by 



1861.J 



