NATUEAL SCIENCES OF PHILADELPHIA. 141 



Surface finely granular. Column round, moderately stout and composed of 

 rather tliin pieces, of uniform size near the base, with a rather small, round or 

 subpentagonal central canal. 



Length of body belovs' 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 through- 

 out. 



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

 general physiognomy of the typical forms of Potei-iocrhiites, but differs in having 

 but two primary radial pieces to each ray, with the sutures between them 

 somewhat gaping, as in Scaphiocrinus. Specifically 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 primary radial pieces to each ray, and hence seems to fall into 

 Scaphiocrinus, giving that group the wide limits usually admitted. The species 

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

 [Scaph.) subimpressus, by not having its body plates impressed at the corners, 

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



Locality arid position. Lower beds of the Burlington group, Burlington, 

 Iowa. Lower Carboniferous. No. 277 of Mr. Wachsmuth's collection. 



Scaphiocrinus nanus, M. and W. 



Body very small, expanding rapidly from the column to the top of the first 

 radials, where it is about once and a half as wide as high. Base small, slightly 

 projecting, pentagonal in outline, and nearly covered by the round, flat facet 

 for the attachment of the column. Basal pieces showing a very short, minute 

 pentagonal facet above the column. Subradial pieces a little wider than long, 

 three with a pentagonal outline, and two on the anal side hexagonal, there 

 being no well defined angle visible at the middle of the under side of any of 

 them. First radials of about the size of the subradial pieces, a little wider 

 than long, pentagonal in form, and somewhat rounded on their outer sides, in 

 cousequence of the sutures between them being impressed. Second radials 

 longer than wide, or nearly twice as long as the first, all pentagonal in outline 

 and rounded and more or less constricted in the middle, each supporting two 

 arms on its upper sloping side. 



Anal pieces consisting of a double alternating series, the lowest one of which 

 rests between the upper sloping sides of two of the subradials, and supports 

 one side of the first radial on the right, while on its left it connects, above the 

 middle, with another anal resting upon the truncated upper side of one of the 

 subradials. and connecting on its left with the first radial on that side; above 

 these three or four other pieces are seen between the arms extending up and 

 joining with the base of the so-called proboscis. 



Arms somewhat rounded on the dorsal side, each bifurcating on the sixth or 

 seventh piece above the second primary radials, and composed of wedge form 

 pieces that are a little longer than wide on the longer side. Above the bifur- 

 cations these pieces are somewhat constricted and each one projecting laterally 

 above, on its longer side, for the reception of the pinnulas, so as to present a 

 rather zigzag appearance. Pinnule moderately stout, and rather distantly 

 separated from each other; composed of joints a little more than twice as long 

 as wide. 



Surface of body plates even, and finely granular. 



Height of body, 0-10 inch to top of first radial pieces, where it measures about 

 0-20 inch in breadth. Arms about 0-75 inch in length. 



In size and general appearance this species is quite similar to S. dichotomus, 

 of Hall, with which it also agrees in having its arms bifurcating but once above 

 their origin on the second radials. It differs, however, in having its second 

 radial pieces rounded instead of angular, and distinctly longer in proportion to 



1869.] 



