544 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



the sides of the inverted cup. Costals large, their knobs very prominent, 

 and arranged witli those of the first interbrachials into a circle, which sur- 

 rounds tlie concavity. Disticlials 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- 

 iriars 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 

 rows of one, two, and three pieces, so arranged as to form, together with the 

 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. 



Horison and Locality. — Hamilton group ; Alpena, Mich. 



Types in the Museum of the Davenport Academy, and in the collection 

 of Wachsmuth and Springer. 



Megistocrinus spinosulus Lton. 

 Plate XLVIII. Figs, la, h, c, and 2. 



1861. Lyon; Proceed. Acad. Nat. Sci. Phila., p. 413, Plate 4, Figs, la, b. 

 1881. W. and Sp. ; Rerisioii P.alffiocr., Part II,, p. 138. 



Sjn. Meijistocriims pileatus — S. A. Miileb, 1879; Ciucm. Soc. Nat. Hist., Vol. II,, p, 114, Plate 

 10, Figs, la, b. 



Of the type of 31. rugosus, but having eight arm openings to the r&y, 

 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. Calj-x 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 

 row; all other plates above and below are slightly convex, except the radials, 

 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. 



