98 DAVENPORT ACADICMY OF NATURAL SCIKNCES. 



DESCRIPTIONS OF SOME NEW CRINOIDS FROM 

 THE HAMILTON GROUP. 



H.Y W. H. BARRIS. 



Presented liefnre tlie Davenport Acatlemj' of Natural Sciences, 1SS3. 



Megistocrinus nodosus. (Revised.) 



Plate I. — Fig. S. A small specimen, showing' side and part of dorsal view. 

 Pr.ATE II. — Fiff- 2. Ventral view of a larg^er individual. 



This species was originally described from a single very imperfect 

 fragment found in Cook's quarry, near Davenport, and figured in Vol. 

 II. of the Proceedings of the Academy. Subsequent discoveries in the 

 same quarry and in Northern Michigan have added to our previous 

 knowledge sufficient material to warrant a more complete description. 



Calyx broadly urn-shaped; the lower truncated part composed of 

 the basals, the first radials, and first anal plate, all nearly in the same 

 plane, the curve rising from the foot of the second radials. Dome 

 composed of numerous small plates, moderately elevated, with marked 

 depressions along the interradial spaces. 



Basals of equal size ; sutures indistinct ; either scarcely extending 

 beyond the column, or expanding into a hexagonal disc, the periphery 

 of which is slightly thickened. 



The first and second primary radials are larger than the third. Sec- 

 ondary radials 2x10 in both antero-lateral rays, which have only two 

 primary arms. The other rays, which have another bifurcation in the 

 calyx, have in place of each second secondary radial, at each side, a 

 tertiary one, and four primary arms. The arms are long, slender, bifur- 

 cating, and composed of a double series of interlocking pieces. 



Interradials numerous; the first hexagonal, and nearly as large as 

 the first radial. There are two plates in the second, third, and fourth 

 rows, all decreasing in size upward. 



The first anal plate resembles the first radials. The second series of 

 anals is composed of three plates, com])aratively large, and these are 

 followed by five, and three i)lates which are more irregularly arranged 

 and smaller. 



