NATURAL SCIENCES OF PHILADELPHIA. 133 



and supports three very small pieces in the next range, which connect with 

 the anal opening, and the vault pieces above, and with the brachials on each 

 side. The vault is made up of a few comparatively large pieces, the central 

 one of which is a little more convex than the others. The anal opening is 

 very small, lateral, or about on the same horizon as the arm openings, and 

 surrounded by only five plates, which are not protuberant. There are twelve 

 small arm openings arranged around the margin of the summit, three to each 

 of the posterior rays, and two to each of the others. The arms would appear, 

 from the small size of the openings, and the very small articulating surfaces 

 for the reception of the first free arm pieces, to be very slender and fragile. 

 (Column unknown.) 



Height of body, C'31 inch., breadth from the anal to the anterior side, 0*42 

 inch ; breadth of base, 0*17 inch. 



This is a very remarkable species, differing from any other Actinocrinus 

 known to us, in the concavity of the under side, and the incurved character 

 of its first anal, and first radial pieces. Its under side presents much the ap- 

 pearance of Zeacrinus, though in the number and arrangement of the parts 

 composing the whole body it will be seen to possess all the essential characters 

 of the great genus Actinocrinus as it is now understood. We place it provi- 

 sionally in the sub-genus Amphoracrinus, on account of the lateral position of 

 the anal opening, but we suspect it should be made the type of a distinct 

 sub-genus. It differs from Agaricocrinus, in having comparatively much 

 larger first radial pieces, as well as in the general form of its body, and its 

 much smaller arms, which are also located around the summit, instead of 

 around the lower part of the body. 



We are under obligations to Mr. Charles Wachsmuth, of Burlington, Iowa, 

 for the use of the only specimen we have seen. 



Locality and position. Burlington, Iowa. Burlington Limestone, of the 

 Lower Carboniferous series. 



Actinocrinus (Pradocrinus ?) amplus. Body large, unshaped, composed of 

 thin, smooth, or finely granulose plates. Base comparatively small, somewhat 

 spreading ; columnar facet large, or between one-half and two-thirds as wide 

 as the base, having a small marginal rim. Column strong, round, and com- 

 posed of thin segments near the body, where it has a very minute round 

 central cavity. First radial plates rather large, a little longer than wide, and 

 all apparently hexagonal, there being no distinct angle at the middle of those 

 alternating with the basal pieces. Second radial plates about two-thirds as 

 large as the first, nearly or quite as wide as long, and all hexagonal. Third 

 radials a little smaller than the second, hexagonal and heptagonal in form, 

 and supporting on their superior sloping sides the two first brachial pieces, 

 which are comparatively large, and each succeeded by three or four much 

 smaller short brachials, before the arms pass into double alternating ranges of 

 small pieces. The first anal plate is as large as the first radials, pentagonal 

 in form, and supports two subhexagonal pieces in the next range, above which 

 there are some twelve or thirteen other smaller pieces of various forms. The 

 first interradial plates are a little larger than the second radials, irregulary hex- 

 agonal, and each surmounted by two rather small pieces in the second range, 

 and three in the next, over which there are six or seven still smaller pieces, 

 making eleven or twelve in each interradial space. 



After the division of the rays on the third primary pieces, the brachials 

 above the first pair curve nearly horizontally outwards, but are included so 

 as to form a part of the walls of the body. Beyond the fourth or fifth brachial, 

 the arms consist of a double row of small alternating pieces, of which there 

 are eight or ten ranges, to a point where the first bifurcation of the free arms 

 takes place. 



Beyond this division, the arms continue to be strong, rounded, and each 

 composed of a double series of short alternating pieces, though the specimen 

 1861.] 



