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604 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Cactocrinus thalia (Hatz). 
Plate LVI. Fig. 2, and Plate LVI. Figs. 12 and 18. 
1861. Actinocrinus thalia —Hatu; Descr. New Spec. Crin. (Prelim. notice), p. 13. * 
1881. Actinocrinus thalia —W. and Sv.; Revision Palwocr., Part IT., p. 146. 
Syn. A. infrequens Hatt; 1861, Descr. New Spec. Crin. (Prelim. notice), p. 14. 
Syn. 4. xodosus 8. A. Mituer; Geol. Surv. Missouri, Bull. No. 4, p. 33, Plate 5, Fig. 7. 
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Of the type of C. proboscidalis. Dorsal cup obconical, nearly as high as 
wide, somewhat constricted below the arm bases. Plates convex, the surface 
covered with radiating ridges and conspicuous nodes. The ridges, which are 
rounded and not very strongly marked, passing out from near the centre of 
the plates to the sides, where they meet the ridges from adjoining plates. 
Three of the radials have three parallel ridges running toward the basals; 
the two others, those resting both upon a basal and the first anal plate, have 
only two, one toward each basal. The ridges between all other plates are 
single. The nodes, which occupy the middle of the plates, are rounded, 
broad, and heavy, rising abruptly from the general surface ; those upon 
radials and brachials transversely arranged. . 
Basals moderately large, forming a spreading cup, provided at the lower 
end with a thickened collar. Radials as long as wide, distinctly angular at 
the lower end. Costals of nearly equal size, one third smaller than the radi- 
als, and both hexangular. Distichals and palmars one, about half the size of 
the costals, the plates of the upper row connected laterally. Arms very long 
and slender, four to the ray; composed of short, smooth plates. Inter- 
brachials at the regular sides, 1, 2, 2, 1; at the anal side 2, 3, 8, 2; the anal 
plate as large as the radials. Interdistichals two, longitudinally arranged. 
Construction of ventral disk and form of anus unknown. Column com- 
a od 
paratively small; axial canal large and pentangular. 
Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa, 
and Sedalia, Mo. | 
Remarks. — This species is most remarkable for the heavy nodes upon 
the calyx plates. It differs from C. proboscidalis in the larger size and more 
conical form of.the dorsal cup, the greater number of interbrachials, the 
presence of interdistichals, its longer and more slender arms, the size of the 
column, and the greater width of the axial canal. | 
