o 



80 PROCEEDINGS OF THE ACADEMY OF 



under side, and provided with a rather broad rounded sinus above for the re- 

 ception of the second radials, the lower margin of the excavation being but 

 very s//ghtly projecting. Second radial pieces small, much wider than long, 

 triaDgular, and about filling the sinus in the upper side of each first radial ; 

 concave on their upper sloping sides, which support the primary divisions of 

 the arms. (Anal and interradial pieces unknown.) 



The arms, after the first division on the second radial plate, bifurcate again 

 on the second piece, and at least two of the inner of these subdivisions, divide 

 once more on the second piece, (in two of the arms examined). Above these last 

 divisions each arm is slender, nearly cylindrical, and consists of a single series 

 of plates for a short distance, then gradually passes into a double alterna- 

 ting series. The tentacles are closely arranged, and rather thick, where they 

 connect with the arm pieces, but soon taper, and appear to be all made up of 

 long slender joints. 



Height from the base to the summit of the first radials, 0-35 in ; breadth at 

 the top of first radials, 0.45 inch; breadth of base, 0-37 inch; height of do., 

 0-13 inch ; height of first radials, 0-24 inch. 



Named in honor of Mr. Henry Pratten, deceased, formerly of the Geological 

 Survey of Illinois. 



Locality and position. Randolph County, Illinois. St. Louis, Limestone of 

 the Subcarboniferous series. 



Platycrinus penicillcs. Body small, subglobose, a little wider than long, 

 Composed of thin plates, connected by moderately distinct sutures, and orna- 

 mented by small tubercles or coarse granules, which, on the first radial plates, 

 show a tendency to range themselves in a few radiating rows from the middle 

 of the upper side. Base comparatively large, much depressed, considerably 

 wider than high, and broadly truncate, with a marginal rim below. First 

 radial pieces large, nearly flat, and a little higher than wide; widening some- 

 what from the base, subquadrangular, the upper angles being slightly truncate 

 by the interradial and anal pieces ; sinus in the upper side for the reception of 

 the second radial pieces shallow, and apparently about half as wide as the 

 superior edge. Second radials small, triangular, wider than long, and support- 

 ing on their upper sloping edges the first divisions of the arms. (Anal and 

 interradial pieces unknown.) 



Above the first bifurcation on the second radial pieces, the two divisions of 

 the arms subdivide on the second piece, and the two middle subdivisions each 

 bifurcate again on the second piece, beyond which they are all simple. Imme- 

 diately above the last bifurcations, the arms consist of a single series of pieces 

 which are somewhat wedge-shaped, or alternately longer and shorter on op- 

 posite sides ; then gradually pass into a double series of alternating joints 

 above. The larger single arm pieces, below the bifurcations, and for a short 

 distance above, are generally longer than wide, narrow around the middle, and 

 broader at each extremity, the superior lateral angles projecting for the recep- 

 tion of tentacles. All the larger arm pieces are connected by peculiar undu- 

 lating sutures. 



The column is comparatively large, and seems to have been very flexible. 

 Near the body it is rounded and composed of thin alternately larger and 

 smaller segments, with sharp edges, which are often crennlated. Farther down 

 it becomes alternately compressed in opposite directions, at intervals of about 

 every five joints ; while all the joints increase somewhat in thickness, and are 

 ornamented with distinct spine-like projecting points or crenulations. About 

 every fifth segment is more prominent on its edges than the others. 



Length of body from base to the summit of the first radials, 0-21 inch 

 breadth, about 0-26 inch ; length of arms, near 0-89 inch 



Locality and position. Hardin County, Illinois. St. Louis Limestone, of th* 

 subcarboniferous seriea. 



Platycrinus plenus, Calyx subglobose, wider than high, composed of thin, 



[Sept. 



