604 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



Cactocrinus thalia (Hall). 

 Plate LVI. Fig. 2, and Plate LVII. Figs. M and 18. 



1861. Adinocrinus thalia — Hall; Descr. New Spec. Crin. (Prelim, notice), p. 13. 

 1881. Aelinocriims thalia — W. and Sp. ; Revision Paleeocr., Part 11., p. 146. 



SjTi. A. infreqiiens Hall ; 1861, Descr. New Spec. Crin. (Prelim, notice), p. 14. 



Syn. A. nodoms S. A. Millee; Geol. Surr. Missouri, Bull. No. 4, p. 33, Plate 5, Fig. 7- 



Of the type of G. 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. Eadials 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, 3, 2 ; the anal 

 plate as large as the radials. Interdistichals two, longitudinally arranged. 

 Construction of ventral di.sk and form of anus unknown. Column com- 

 paratively small ; axial canal large and pentangular. 



Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa, 

 and Sedalia, Mo. 



Eemarhs. — This species is most remarkable for the heavy nodes upon 

 the calyx plates. It differs from C. prohoscidalis 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. 



