Soe 
544 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
the sides of the inverted cup. Costals large, their knobs very prominent, 
and arranged with those of the first interbrachials into a circle, which sur- 
rounds the concavity. Distichals rather large, consisting in the antero-lateral 
rays of two or three plates, which form the bases of two primary arms; the 
three other rays have a single plate, which is axillary and supports two pal- e 
mars from each side and two arms, thus making sixteen primary arms to the 
species. The arms are not preserved in the specimens, but, to judge from 
| the size of their facets, were moderately stout. Interbrachials disposed in 
aS ieee 
rows of one, two, and three pieces, so arranged as to form, together with the 
ae | first and second costals, respectively, two well defined circlets of plates 
around the radials. Anal interradius considerably wider, and made up of 
a greater number and smaller plates. Ventral disk highly elevated, sub- | 
conical; the orals and radial dome plates larger than the surrounding plates, 
and extended into short spines; the surrounding plates tuberculous. Anus ! 
almost central. Column of medium size; the axial canal wide and obtusely | 
pentangular. | 
th Horizon and Locality. — Hamilton group; Alpena, Mich. 
er 1 Types in the Museum of the Davenport Academy, and in the collection 
of Wachsmuth and Springer. 
Megistocrinus spinosulus Lyon. 
Pip ods VIII. Figs. 1a, b, c, and 2. “S 
1861. Lyon; Proceed. Acad. Nat. Sci. Phila., p. 418, Plate 4, Figs. 7a, 0. 
1881. W. and Sp.; Revision Paleocr., Part II., p. 188. 
Syn, Megistocrinus pileatus —S. A. Mrutmr, 1879; Cincin. Soc. Nat. Hist., Vol. IL., p. 114, Plate 
10, Figs. la, &. 
| 
: ° : | 
Of the type of M. rugosus, but having eight arm openings to the ray, 
which are arranged in a continuous row around the calyx, and not in 
| 
groups; the basals slightly projecting instead of concave, the radials more 
depressed, and the anal tube more excentric. Calyx short in proportion to 
its width, which at the arm bases is almost twice its height; truncated to the 
middle of the second costals. The latter plates, and the interbrachials of the 
second row, are extended into very conspicuous tubercles, and somewhat | 
| shorter tubercles mark the first distichals and the interbrachials of the third : 
Hi | row; all other plates above and below are slightly convex, except the radials, | 
Mi which are a little concave. The sides of the dorsal cup stand almost at 
right angles to the base, expanding slightly to the arm bases. Ventral disk 
low, a little convex, somewhat bulging at the posterior side. 
