470 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



enclose a large interdistichal. Column composed of large and small joints, 

 the larger or nodal joints increasing in width downward, and at 4 cm. from 

 the calyx are twice as wide as the intervening pieces; they are also much 

 longer and angular at their outer edges. 



Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa, 

 Sedalia, Mo., and Lake Valley, New Mexico. This is one of the most char- 

 acteristic species of the lower Burlington division. 



Memarks. — Adinocrinus trieoniis &.ViA A. jjenclens, both described by Hall, 

 are nndoubtedly specifically identical with Dorycrinus unicornis. In the first 

 the posterior radial dome plates are extended into spines ; in the second the 

 nodes of the radials and first anal plate are " elongate and subclavate, being 

 contracted in the middle, and swelling out at the extremities." Among this 

 variety also we find specimens with one, two, or three spines upon the ven- 

 tral disk, which are comparatively longer in young specimens. In the speci- 

 mens from Pike Co., Mo., described by Rowley and Hare as Dorycrinus 

 inflatus, the plates of the dorsal cup are less angular than usual in this 

 genus. 



AOROCRINUS W. and Sp. (nov. gen.). 



('Aciipo5 immature, xpivov a lily.) 



The species small. Form of the calyx and arrangement of the plates 

 similar to Dori/crinus. As in that genus, the arms are arranged in groups, 

 and vary in number among the rays, the anterior ray generally having 

 the fewest. The arms are stout and packed closely together, there being 

 invariably but one arm from each ambulacral opening in the calyx. The 

 ventral disk, as a rule, is shorter than the dorsal cup, the jDlates are smooth 

 or slightly convex, except the posterior oral, which is more or less elevated 

 and frequently tuberculiform, but not actually spinous. The ambulacra are 

 tegminal, and covered with two rows of small pieces. The anal area is com- 

 posed of small plates, generally forming a protuberance or low ridge, which 

 slopes downward almost in a straight line from the edges of the posterior 

 oral to the first anal plate. The anus is placed near the upper end, and 

 faces laterally. 



Distribution. — This genus occurs in America in the Hamilton, Kinder- 

 hook, and in both divisions of the Burlington group. It survived to the 

 Keokuk group, where it is represented by only a single species. In Europe 

 it is possibly represented by " Actinocrinus " prumiensis Miiller, from the De- 



