472 THE CKINOIDEA CAMEEATA OF NORTH AlVIEEICA. 



times as wide. Iiiterbrachials three ; the first very large, as wide as high, 

 the two upper quite small. They are followed by two still smaller pieces, 

 which are on a level with the arm bases, and these by equally small inter- 

 ambulacral plates ; there being no interdistichals in the dorsal cup, but several 

 in the tegmen between the ambulacra. First anal plate much longer than 

 the radials, and the largest plate of the dorsal cup. It is followed by three 

 or four higher anals, longitudinally arranged, which decrease rapidly in size 

 upward, each one having an interbrachial at the sides. There are numerous 

 plates above, which form a longitudinal ridge with a deep sulcus at each 

 side. The anus, which is placed at the upper end of this ridge, opens out 

 laterally. Orals a little more convex than any of the other plates of the 

 tegmen ; the posterior one very large, its size equal to that of two of the 

 others, and generally extended into a short spine. Food grooves covered by 

 a few alternately arranged medium-sized plates, which are more prominent 

 than the interambulacrals, especially on approaching the arms. Column com- 

 paratively short, gradually tapering, and terminating as a fine thread ; its 

 whole length being from 7 to 9 cm. The joints throughout are moderately 

 long, and increase in length downward. They are in the upper part of the 

 stem distinctly rounded at their margins, and project conspicuously over the 

 younger joints ; but at the lower part cylindrical and of equal width, giving 

 off toward the end at irregular intervals, and at different sides, rather stout 

 and long cirri. 



Horizon and Locality. — Kinderhook group; Le Grand, Marshall Co., 

 Iowa. 



Types in the collection of Wachsmuth and Springer. 



Aorocrinus radiatus w. and Sp. 



Plate XLV. Fig. 1. 



1890. Donjcrinus radiatus— W. and Sp. ; Geol. Rep. Illinois, Vol. VHI., p. 176, Plate 17, Figs. 5, 5a. 

 1890. Dorycrima radiatus S. A. Miller; N. Amer. Geol. and Palaeont., p. 240. 



Eesembling the preceding species, but having a different arm formula, and 

 radiating ridges upon the plates. From the radials two low, rounded ridges 

 pass out to the basals, two to adjoining radials and the first anal plate, and 

 one to the first interbrachials. The latter plates have nine ridges, two meet- 

 ing with those from the radials, the others, which are somewhat smaller^ with 

 tlie costals and the interbrachials of the second range. The ridges are well 



