34 



as the third radial. It is presumed that it was followed by two 

 small plates, but they are not preserved in either of our specimens. 



This species is so different from all the species heretofore 

 described that even a fragment of it can be distinguished, and no 

 comparison, therefore, with either of them is necessary. 



Found in the Niagara Group, at St. Paul, Indiana, and now in 

 the collection of Wm. F. E. Gurley. 



Family RHODOCKINID^. 



ARCELEOCRINUS KNOXENSIS, n. Sp. 



Plate III, Fig. 10, basal view; Fig. 11, azygous view; Fig. 12, 

 summit view, the matrix covers the sutures of some of the plates. 



Species rather large. Calyx bowl-shaped, subpentagonal in out- 

 line, about one-half wider than high. Radial ridges not defined. 

 Plates highly convex and each one bearing a central node and 

 some of the largest plates bearing two or three nodes. Sutures 

 beveled. Surface granular. Columnar cavity rather small and 

 subpentagonal in outline. 



Basals email and hidden by the column. They form a small 

 cup which is filled with the end of the column, and on the top of 

 which the subradials rest. Subradials large, longer than wide, 

 abruptly bent into the columnar cavity and upward between the 

 under sloping sides of the first radials. The azygous subradial is 

 octagonal, the others heptagonal, by reason of three 'plates in the 

 azygous area touching the subradial, while only two touch it in 

 the other areas. The summit is not truncated in the regular 

 areas and only minutely in . the azygous area. The first primary 

 radials are smaller than the subradials, about as high as wide; 

 each one is heptagonal. The inferior angle is sunk in a pit 

 formed by it and the adjacent lateral angles of the subradials. 

 Second primary radials more than half as large as the first, three 

 heptagonal and two hexagonal, each one wider than long. Third 

 primary radials very small, of unequal size, generally about one- 

 third as large as the second primary radials, one hexagonal, the 

 others pentagonal, axillary, and support on each upper sloping 

 side two small secondary radials. There are, therefore, ten arms 

 in this species and ten ambulacral openings to the vault. There 

 are no intersecondary radials. 



