582 THE CEINOIDEA CAMEKATA OF NORTH AMERICA. 



Steganocrinus concinnus (Shumaed). 

 Plate LXI. Figs. 5a, I. 



1855. Actimcrims coiichimis — Shdm. ; Geol. Surv. Missouri by Swallow, Part 11., p. 189, Plated, Pig. 5. 

 1866. Actimcdnus conciums — Meek and Woktuen; Geol. Rep. Illinois, Vol. II., p. 200, Plate 15, 



Pigs. 9«, b. 

 1881. Steganocrinus concinmis — W. and Sp.; Revision Palseocr., Part IP, p. 151. 



Syn. AcHnocrims validus — Meek and Wokthen ; 1860, Pro.ceed. Acad. Nat. Sci. Pbila., p. 384. 



Another species closely related to S. 2^ent(igonus, but larger, the plates 

 more robust and of different proportions, the first costals comparatively 

 smaller, the second much shorter and smaller generally, the basal cup deeper. 

 Calyx nearly as high as wide, convex at the sides, distinctly lobed at the 

 top of the first costals, the interradial spaces between the brachial trunks 

 extremely wide and depressed, the marginal part of the ventral disk con- 

 stricted, the middle to the base of the anal tube almost flat. Dorsal cup 

 decidedly convex, thick and heavy in the middle portions, thinning out 

 toward the margins. The edges of the plates marked by low, rounded 

 ridges, which either in single series ot in groups of two or four traverse the 

 suture lines, and proceed to the margins of adjoining plates, leaving the 

 greater part of the plates perfectly smooth. The ridges are not only surface 

 elevations, but originate in part from a folding of the plates themselves ; 

 they extend only to the centre of the first costals and second interbrachials, 

 not to the upper portions of these plates, nor to any of the plates above. 



Basals large, forming a spreading cup, with well defined snture lines, and 

 sharpily angular lower margins. Eadials about as wide as high, considerably 

 larger than both costals together. First costals generall};- about half the size 

 of the radials, hexangular, the sides inflected at the upper end, the upper 

 lateral faces longer than the lower, the upper faces nari'ow, semicircular, 

 concave, and perforated. Second costals hexangular, very short, curved like 

 arm plates, their upper angles obtuse. The higher brachials are not pre- 

 served in the specimens, but the general structure indicates that they formed 

 two trunks from each ray with an oval cavity. First interbrachial as large 

 as, or larger than, the first costals, followed by four plates, which are about 

 level with the appendages ; the two outer ones a little the smaller, bending 

 outward, and in part interambulacral. Anal plate smaller than the radials, 

 supporting two plates in the first, and five in the second range. Ventral 

 disk very slightly elevated, the plates convex, the anal tube somewhat excen- 



