416 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
and tuberculous; the orals and radial dome plates a little more prominent, 
but not much larger than the others. Anal tube almost central, compara- 
tively narrow, and rising but little above the tips of the arms. Column 
rather stout, the joints rounded at their edges; the nodal joints quite 
prominent, 
Horizon and Locality. — Keokuk group; Crawfordsville, Ind. 
Types in the Lyon collection at Jeffersonville, Ind. 
fiemarks. — Specimens in which single arms are placed between the 
paired ones are very rare in this species. Among over forty specimens 
in our collection we found but two. One of them has seventeen paired 
arms and one single one, the other twelve single and six paired ones. The 
latter specimen is so interesting that it deserves special description, and we 
give an illustration of its posterior side (Plate XXXV., Fig. 5). What is 
most remarkable is that the arms differ greatly in width and length; seven 
of the single ones are twice as strong as the three others, and one fourth 
longer; the latter three having the same dimensions as the paired ones. 
The arrangement is shown by the following formula: 
Posterior rays: 1 large, 2, 2, 2;—1 small, 1 large, 1 small, 2. 
Antero-lateral rays: 1 small, 1 large, 1 large, 1 large; —J small, 2, 1 
small, 2. 
Anterior ray: 1 large, 1 large. 
It is possible that this specimen originally had single arms, and that some 
of them were accidentally broken and replaced by paired ones. 
Dizygocrinus indianensis, var. simplex W. and Spr. (nov. var.). 
Plate XX XIII. Fig. 7. 
Somewhat smaller than the typical form. In the proportions of the 
calyx, the ornamentation, and in the arrangement of the plates to the 
top of the distichals, the two forms are almost identical; but in the form 
under consideration only two rows of the palmars are incorporated into the 
calyx, against three in the typical form; the third is a free arm plate; the 
fourth, in place of being a diminutive axillary, is large and cuneate, and sup- 
ports but one arm. There are eighteen single arms, distributed among the 
rays in exactly the same way as the double arms in the other. The arms 
have the same file-like appearance, but are proportionally a little stouter. 
Horizon and Locality.— Same as last. Extremely rare; we have only 
seen a single specimen, which is in our collection. 
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