BATOCRINIDiE. 537 



Megistocrinus nobilis W. and Sp. 

 Plate XLVII. Fkjs. 6, 7, 8a, b, and Plate LI. Fig. 8. 



1890. W. and Sp.; Geol. Eep. Illinois, Vol. Till., p. 169, Plate 16, Figs. 6 and 7. 

 1890. S. A. MiLLEB ; Nortli Amer. Geol. and PalEeout., p. 260. 



Syn. Megistocrinus parvus W. and Sp. ; Geol. Rep. Illinois, Vol. VIII., p. 171. 



Somewhat smaller than the preceding species. Calyx subglobose, nearly 

 as wide as high ; the tegmen depressed hemispherical. Dorsal cup to the 

 middle of the radials slightly flattened, but still convex ; the costals and 

 proximal distichals gently curving ; the higher brachials bending outward 

 and curved transversely, forming ten lobes around the calyx, correspond- 

 ing to the main divisions of the rays. Plates heavy, a little concave ; suture 

 lines somewhat grooved, those between the basals and radials deeper than 

 the others. 



Basals small, forming a hexagon, of which only a narrow rim is visible 

 beyond the column. Radials hexangular in outline, a little wider than long, 

 the upper and lower lateral faces of equal length. First costals as large as 

 the radials ; the two posterior ones pentangular, the others hexangular. 

 Second costals smaller than. the fii'st, and pentangular. First distichals as 

 large as the axillary costal ; those of the second row somewhat smaller ; suc- 

 ceeding distichals biserial, the plates alternating, and decreasing rapidly in 

 leno-th upward. There are four plates in one series and five in the other, 

 both followed by two series of short transverse palmars, which to the third 

 plate talce part in the calyx, and bifurcate again above the fifth or sixth. 

 Arm facets arranged in ten pairs, large, and directed upwards. Arms short 

 in proportion to the size of the calyx, bifurcating three or four times, the 

 tips infolding ; they are robust at their bases, but diminish in size with each 

 bifurcation, and are composed of moderately short pieces. Pinnules short 

 and rarely preserved. Regular interbrachials in five or six ranges : 1, 2, 2, 

 3, 3, 2, with slight variations. Interdistichals in three or four rows; the 

 first generally resting upon the second distichals, rarely upon the first. The 

 first anal plate longer than the radials ; the three plates above as large as 

 the first interbrachial of the other sides ; followed by four or five plates, and 

 these by numerous others of indefinite arrangement. Ventral disk from 

 almost flat to moderately convex ; the plates flat, of almost uniform size 

 and irregular arrangement. The orals, if represented at all, indeterminable, 



68 



