582 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Steganocrinus concinnus (SuumAzrp). 
Plate LXI. Figs. da, 0. 
1855. Actinocrinus concinnus—Suvum.; Geol. Surv. Missouri by Swallow, Part IL., p. 189, Plate 4, Fig. 5. 
1866. Actinocrinus concinnus —Mnnx and WortuEen; Geol. Rep. Illinois, Vol. IL., p- 200, Plate 15, 
Figs. 9a, 0. 
1881. Steganocrinus concinnus— W. and Sp.; Revision Paleocr., Part IL., p, 151. 
Syn. Actinocrinus validus — Mux and WortHEN; 1860, Proceed. Acad. Nat. Sci. Phila., p. 384. 
Another species closely related to S. pentagonus, 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 or 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 suture lines, and 
sharply angular lower margins. Radials about as wide as high, considerably 
larger than both costals together. First costals generally 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 narrow, 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- 
fi 
a) 
