416 THE CEINOIDEA 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. 



Remarks. — 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 

 arras 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 ; — 1 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 Sp. (nov. var.). 

 Plate XXXIII. 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 

 imder 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. 



Horison and Locality. — Same as last. Extremely rare ; we have only 

 seen a single specimen, which is in our collection. 



