1<30 PROCEEDINGS OF THE ACADEMY OF 



Genus CYATHOCRINUS, Miller, 1821. 



Cyathocrintjs arboreus, M. & W. 



Body rather under medium size, conoidal-semiovate below the top of the 

 first radial pieces, about as wide as high. Basal pieces well developed, form- 

 ing a low basin-shaped cup; all pentagonal, and about as long as wide, the 

 greater breadth being slightly above the middle. Subradial pieces three or 

 four times as large as the basal, about as long as wide, usually arcuate, or 

 a little concave on the outside along the lateral margins four hexagonal and 

 one heptagonal. First radial pieces of near the same size as the subradials, 

 ar.d presenting a more or less nearly pentagonal outline ; facet for the recep- 

 tion of the second radials nearly equalling one-third the breadth of the first 

 radial pieces, slightly protuberant, and sloping outwards. Succeeding radials 

 small, rounded on the outside, and varying from two to five in the different 

 rays; there being but two in one of the posterior rays and five in the other, 

 while the anterior ray has four, one of the antero-lateral three, and the other 

 four, all excepting the last or axillary piece being quadrangular. 



After the first division into two arms on the fourth primary radial piece, (at 

 least in one of the antero-lateral rays,) another division immediately takes 

 pla "e on the first piece of each principal branch, and of the four branchlets 

 thus foumed, the inner two ascend directly upwards, and each bifurcates again 

 on the second piece, and the subdivisions each again on the third piece; while 

 the two main lateral branchlets spread out on either side, each giving off above 

 two or more subordinate branchlets, the first of which is seen to bifurcate at 

 least once. The whole of the divisions and subdivisions being thus spread out 

 to as to resemble the trained limbs of a tree spread upon a wall. The divisions 

 of the other rays cannot be traced out in the specimen examined, in the same 

 detail, but some e>f them appear to divide much in the same way, and others 

 somewhat differently. 



All the arms and their divisions aie rounded, and the smaller divisions com- 

 posed of joints that are longer than wide, while no tentacles have been observed 

 connected with any of them. 



The first anal piece is quadrangular, a little longer than one of the basal 

 pieces, and rests directly upon the superior truncated side of one of the sub- 

 radials, while it connects on each side with one of the large first radial pieces, 

 above which it does not project. Other anal pieces unknown. 



The sutures are slightly impressed, and the surface nearly smooth, or only 

 obscurely granulose. The column and summit are unknown. 



Height to summit of first jadial pieces, 0-66 inch, on the anal side, and 0*55 

 inch on the other; breadth at top of first radial pieces, 0-53 inch ; breadth of 

 second and succeeding primary radial pieces, 015 inch. 



Locality and position. Crawfordstille, Indiana. Keokuk division of Sub- 

 carboniferous series. 



Genus PLATYCRINUS, Miller, 1821. 



As first proposed by Miller, this genus was badly defined, and it is manifest 

 that its author himself, had no very clear ideas of its limits, since he also in- 

 cluded in it species of Pentremites, Say, Dichocrmus, Munster, and of his own 

 genus Actinocrinus. Later writers, however, have restricted it within far more 

 natural limits, and, as now generally understood, Miller's first species, P. Icevis, 

 seems to be regarded as the typical form of the genus. In this and the closely 

 allied species, the body is more or less hemispherical below the arms, while 

 the dome terminates above in a long, generally slender, central or subcentral 

 proboscis, closed at the summit, but apparently pierced by a small aperture on 

 one side near the upper extremity. In these typical forms the arms bifurcate 

 once or oftener near the body, beyond which they are simple, and composed 

 at first, of a single series of wedge-shape pieces, passing more or less gradually 



fAug. 



