416 PALEONTOLOGY OF ILLINOIS. 



and constricted in the middle, with a pentagonal outline 

 (excepting the one in the anterior ray, which is truncated 

 above,) and supporting the arms on their superior sloping 

 sides. Arms nine or ten, simple from their origin, very 

 long, slender, rounded and composed of wedge-form pieces, 

 which have their longer side about twice the length of the 

 shorter, and equaling their breadth, but not projecting so 

 as to give the arms a zigzag appearance. Pinnulse long, 

 moderately stout, and composed of joints about twice as 

 long as wide. Anal pieces unknown. 



Surface finely granular. Column round, moderately stout 

 and composed of rather thin pieces, of uniform size near the 

 base, with a rather small, round or subpentagonal central 

 canal. 



Length of body below the summit of the first radial pieces, 

 0.40 inch; breadth, about 0.50 inch; diameter of column at 

 base, 0.18 inch; entire length of arms unknown, as they 

 are all broken at the extremity, with the remaining portion 

 measuring 3.40 inches in length, with thickness of about 

 0.10 inch throughout. 



This species has the long, straight arms, obconic body, protuberant 

 base, and general physiognomy of the typical forms of Poteriocrinites, 

 but differs in having but two primary radial pieces to each ray, with 

 the sutures between them somewhat gaping, as in Scaphiocrinus. Spe- 

 cifically it is not closely allied to any of the other known species. In 

 the form of its body it is most nearly allied to our Pot. subimpressus, 

 which, Mr. WACHSMUTH has ascertained, probably has only two prim- 

 ary radial pieces to ea'ch ray, and hence seems to fall into Scaphiocrinw, 

 giving that group the wide limits usually admitted. The species here 

 under consideration, however, will be readily distinguished from the Pot. 

 (Scaph.) subimpressus, bj T not having its body plates impressed at the 

 corners, and all distinctly thinner, as well as by its less robust general 

 habit. 



Locality and position Lower beds of the Burlington group, Bur- 

 lington, Iowa. Lower Carboniferous. No. 277 of Mr. WACHSMUTII'S 

 collection. 



