MELOCRINID^. 307 



Distribution. — Allocrijius is restricted to America. It belongs to a little 

 group of Crinoids whicli is sparingly represented in this country, but of which 

 several genera with a number of species are known to have existed during 

 the Upper Silurian period in Sweden and England. 



Remarlcs. — This genus has close affinities with Patelliocrinus and Dolato- 

 crinus. It differs, however, from both of them in the form and size of the 

 various calyx plates, and in having uniserial arms. It also approaches Cen- 

 trocrinus, but this has a large and perfectly anchylosed basal disk. 



AUocrinus typus W. and Sp. 



Plate XXIV. Figs. 7a, h. 



1889. W. and Sp. ; Geol. Rep. Illinois, Yol. YIII., p. 207, Plate XIV., Fig. 7. 



Below medium size. Calyx depressed, proportionally small, sharply 

 pentangular in outline, the arm bases projecting, the arms massive and 

 proportionally stouter than those of any other Crinoid; the plates with- 

 out ornamentation. Basals small, forming a flattened disk, which is almost 

 covered by the column ; interbasal and basi-radial sutures indistinct. Kadials 

 large, abruptly curved, the lower portions forming the rim of an inverted 

 shallow basin, the upper half bent abruptly upward and forming together 

 with the plates above a shallow, spreading cup with straight sides. Costals 

 and fixed distichals short, curved like arm plates, producing upon the sur- 

 face of the calyx strong, rounded ridges, which insensibly pass into the free 

 arms. Arms ten, stout, uniserial, free above the second plate ; composed of 

 transverse joints with parallel upper and lower faces. The arms much wilder 

 midway than at either end, tapering considerably and uniformly toward the 

 tips, but almost as much toward the calyx. Interradial spaces deeply de- 

 pressed, composed of two plates vertically arranged, of which the first is the 

 larger and nodose, and extends to the top of the costals ; while the other is 

 on a level with the fixed brachials, and forms, to some extent, a part of the 

 ventral surface. Nothing is known of the anal aperture and the structure 

 of the ventral disk. Column round, small • axial canal pentangular. 



Horizon and Locality. — Niagara group ; Wayne and Decatur Cos., Tenn. 



T?/pes in the Worthen collection, Springfield, and that of Wachsmuth and 

 Springer. 



