132 PROCEEDINGS OF THE ACADEMY OF 



cylindrical from the base to the top of the third radial plates, above which 

 the secondary radial and brachial pieces curve abruptly outwards to the base 

 of the arms, so as to form with the ventricose summit a much expanded vis- 

 ceral cavity, entirely above the basal and primary radial plates. Base un- 

 known ; first radials unknown, excepting from some remaining portions of 

 their upper ends, which show that they are comparatively large. Second 

 radials very small, a little wider than long, (those seen) irregularly pentagonal 

 in form, one of the sides being much shorter than the others. Third radials 

 as long as the first, and nearly one-third wider, (the only two visible in our 

 specimen,) hexagonal in form, and each supporting on its superior sloping 

 sides two secondary radials of about its own size. Each of these is surmounted 

 by a somewhat larger second secondary radial, which in its turn supports two 

 first brachial pieces, each of which is succeeded by a second, from which the 

 free arms are given off. The two series of secondary radials, and the fmr 

 series of brachial pieces in each ray, connect laterally, so as to leave 

 no room for interaxillary and interbrachial pieces. Interradial plates two or 

 three, the first being about the same size as the second radials, and hexagonal 

 or heptagonal in form. Above this there are one or two small pieces, of variable 

 size and form, over which the secondary radials, and the lateral series of bra- 

 chial pieces of the rays on each side, connect all the way up to the free arms, 

 in such a manner as to leave no spaces for interradials above those just descri- 

 bed. (Anal plates unknown.) 



Dome hemispherical, composed of pentagonal, hexagonal, and heptagonal 

 plates of nearly uniform size, each of which is provided with a spine-like 

 tubercle. Proboscis central or nearly so. Arm openings twenty. Surface 

 smooth or obscurely granulose ; small rather pointed tubercles are also seen 

 on the second and third radial plates, first interradials, and first secondary 

 radials. 



It is possible this Crinoid may be specifically distinct from A. pyriformis, of 

 Shumard, but it agrees with it in so many respects that we do not feel fully 

 warranted in regarding it as specifically distinct. Its most important differ- 

 ences are the sub-spiniferous character of its plates, and the possession of only 

 two or three interradial plates, instead of six in each interradial space. It 

 also differs in having a more ventricose dome, while the inferior half of its 

 body is more abruptly contracted below the arms. 



Locality and position. Salt Lick Point, Monroe County, Illinois. Where it 

 occurs in beds of the same age as the Chouteau Limestone of Prof. Swallow. 



Actinocrinus (Amphokacrinus ?) cofCAvcs. Body small, subglobose, broader 

 than high, a little oblique ; summit nearly flat ; under side rounded and dis- 

 tinctly concave, sides rising vertically or nearly so. Surface smooth or sub- 

 granulose. Base small, concave, and entirely included within the concavity 

 of the under side. First radial plates comparatively large, convex, and curv- 

 ing under, so as to form a part of the concavity below ; two of them hept- 

 agonal, and three hexagonal. Second radial pieces (wanting in two of the rays 

 of the specimen before us,) wider than long, and quadrangular in form in the 

 others. 



Third radial pieces smaller than the second, (in three of the rays, ) pent- 

 agonal in form, and each supporting upon its superior sloping sides the first 

 brachial pieces, which form a part of the walls of the body. First interradial 

 pieces, comparatively large, or about one-half the size of the first radial plates, 

 nine-sided, the superior sloping sides of each supporting one side of two of 

 the brachial pieces, while two very small pieces rest upon the middle of the 

 summit, and connect with the vault above, and with the brachial pieces on 

 each side. First anal piece a little larger than the first radials, heptagonal in 

 form, and supporting in the next range three pieces, the two lateral of which 

 are larger than the other, and connect above on their sloping sides, with 

 brachial pieces, while the middle piece between these is irregularly hexagonal, 



[June, 



