BATOCRINID&. 533 
Remarks. — We have not been able to trace the type of Megistocrinus 
Knappt, having searched for it in vain in the Knapp 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 Periechocrinus and Abacocrinus, is very characteristic of 
the three genera, which are otherwise well distinguished from each other. 
This arm structure occurs also in Actinocrinus when there is a bifurcation 
beyond the calyx, and in some of the Rhodocrinide. 
Megistocrinus Evansi O. and Suum. 
Plate XLVIT. Figs. 1a, b, 2a, b, 3, Za, b, da, b, e. 
1850. Owen and Saumarp; Journ. Acad. Nat. Sci. Phila., Vol. IL, p. 68. 
1852. Owrn and Smumarp; U.S. Geol. Surv. Wisc., Iowa and Minn., p. 594, Plate 54, Figs. 3a, 4. 
1881. W. and Sp.; Revision Paleocr., Part II., p. 187. 
Syn. Actinocrinus brevicornis — Haut; 1858, Geol. Rep. Iowa, Vol. I., Part IL, p. 571, Plate 10, 
Figs. 4a, 6 (Megistocrinus brevicornis W. and Sp.). 
Syn. Actinocrinus superlatus — Hatt; 1858, ibid., p. 572. 
Syn. Actinocrinus minor —Hati; 1858, ibid., p. 573. 
Syn. Megistocrinus plenus — Wuitx, 1862, Proceed. Bost. Soc. Nat. Hist., Vol. IX., April number 
(Author’s Ed., p. 16). 
Syn. Megistocrinus parvirostris — Muzx and WortHEN ; 1869, Proc. Acad. Nat. Sci. Phila., p. 165, 
and Geol. Rep. Illinois, Vol. V., p. 396, Plate 6, Fig. 7. 
Attaining very large 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 
