578 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



first, and two in the second row. Ventral disk liigbly elevated and bulging 

 at the outer mai'gins, where the plates stand erect. Orals nodose, pushed 

 over to the anterior side, and in the larger specimens separated by accessory 

 pieces. Radial dome plates as large as the orals, strongly nodose and some- 

 times subspinous. The interambulacral plates in contact with the inter- 

 brachials. Anal tube subcentral, rather large at the base. 



Horizon and Locality. — Chouteau Umestone ; SedaUa, Mo. 



Types in the collection of F. A. Sampson, Sedalia. 



Beynarks. — This species is closely related to Acttnocrinus {Blcnrocrinus) 

 trijugis, if not identical with it. Miller claims the latter species has eight 

 arms to the ray, and the other but four, neither of vhich is clearly shown 

 by the specimens. However, there can be no doxibt that Miller's " Blairo- 

 crinus " huUahcs is identical with this species. We examined a number of 

 specimens from the collection of Mr. Sampson, some of which were labeled 

 by Miller B. arrosus, others B. hiillatus, and found that he had described the 

 plumper specimens as B. buUatus and the crushed ones as B. mro&us. We 

 also became convinced that the anus of this species is not so excentric as it 

 appears in Miller's figures, which repi-esent it when pushed out of place 

 by oblique pressure, but that its position is almost central. This is clearly 

 shown by Mr. Sampson's beautiful specimen, of which we give three figures 

 on Plate LV., Figs. 8a, h, c. 



STEGANOCRINUS Meek and Woethen. 



1866. Meek and Woethen ; Geol. Rep. Illinois, Yol. 11., p. 195, also ibid. Tol. IH., p. 47i. 

 1879. ZiTTEL (subgenus of Actinocrims) ; Handb. d. Palseont., Tol. I., p. 370. 

 1881. W. and Sp. ; Revision Palajocr., Part II. , p. 149 (Proceed. Acad. Nat. Sci. Phila., p. 323). 

 1889. S. A. Millek; N. Amer. Geol. and Palaiont., p. 282. 



Syn. Actinocrinm ; Shumaed, 1855; Hall, 1860; Meek and WoKTHEN, 1860. 



In its general structure resembling Actimcrimis, but the rays, instead of 

 being produced into mere lobes, are formed into arm-like, tubular extensions 

 or trunks, which rise to the full length of the crown, giving off armlets alter- 

 nately from opposite sides. There are either one or two of these brachial 

 trunks to the ray, according to species, depending on whether they take 

 their origin from the costals or distichals ; they were apparently rigid, and 

 movable, if at all, only as a whole. The dorsal side of these appendages is 

 formed by a longitudinal row of axillaries, or by a succession of syzygies, in 

 which latter case the second plate of the various orders is arm-bearing. 



