BATOCEINIDiE. 533 



EemarTis. — We have not been able to trace the type of Ifegistocriims 

 Knappi, having searched for it in vain in the Knapjs collection at New Provi- 

 dence, Ind., and in the Lyon collection ; and we omit describing it, as the 

 figures in the Proceed, of the Soc. Nat. Sci. Phila. are somewhat misleading. 



The branching of the arms in their biserial state, whereby there are 

 two rows of interlocking joints below the first bifurcation, as it occurs in 

 this genus and in Periccliocrinus and Ahacocrinus, is very characteristic of 

 the three genera, which are otherwise well distinguished from each other. 

 This arm structure occurs also in Adinocnmis when there is a bifurcation 

 beyond the calyx, and in some of the Khodocrinidoe. 



Megistocrinus Evansi 0. and Shum. 



Plaie XL VII. Figs, la, b, 2a, h, 3, 4a, b, 5a, I, c. 



1850. Owen and Shumaed; Joum. Acad. Nat. Sci. PHla., Vol. II., p. 68. 



1852. Owen and Smtjmard; U. S. Geol. Surv. Wise, Iowa and Minn., p. 594, Plate ZA, Figs. 3«, b. 



1881. W. and Sp. ; Eevisiou Palajocr., Part II., p. 137. 



Sjn. Aciiiiocrinus brevicomis — Hall; 1858, Geol. Hep. Iowa, Vol. I., Part II., p. 571, Plate 10, 



Figs. 4tf, b {^Megistocrinus brenicortiis W. and Sp ). 

 Syn. Actinocrinus superlaius — Hall; 1858, ibid., p. 572. 

 Sjn. Actinocrinus minor — Hall; 1S58, ibid., p. 573. 

 Sjn. Megistocrimis pleniis — White, 1862, Proceed. Bost. See. Nat. Hist., Vol. IX., April number 



(Author's Ed., p. 16). 

 Syn. Megistocrinus parvirosiris — Meek and-WoRTHEN ; 1869, Proc. Acad. Nat. Sci. PhUa,, p. 165, 

 and Geol. Rep. Illinois, Vol. V., p. 396, Plate 6, Pig. 7. 



Attaining very lai-ge size. Calyx wider than high, truncated to near the 

 top of the radials ; basi-radial sutures broadly and deeply channeled ; basals 

 more or less depressed, rarely rising beyond the plane of the radials ; sides 

 of the dorsal cup evenly spreading to the top of the costals, and more 

 abruptly thence to the arm bases. Plates heavy, a little convex, the surface 

 smooth or slightly corrugated, the suture lines deeply canaliculate. 



Basals closely anchylosed ; horizontal, rounded off toward the basi-radial 

 sutures, forming a nearly flat hexagon pierced by a large pentalobate canal ; 

 the column occupying about one half its diameter. Radials wider than long, 

 all hexagonal in outline ; their lower faces parallel with the upper ; upper 

 and lower sloping faces about equal. First costals hexagonal, as long as the 

 radials, but somewhat narrower; the second smaller and pentangular. The 

 axillary costal supports at each side two large distichals, followed by palmars, 

 of which the two proximal ones at either side of the axillary are nearly as 

 long as wide, comparatively large, and those of the same ray interlock at 



