722 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



hidden. The covering plates of the ambulacra proceed from the outer sides 

 of the orals to the ends of the appendages ; they are snturally connected 

 throughout their full length, and form, together with the plates of the dorsal 

 side, almost rigid tubes. Those of the disk are large, as long as wide, and 

 their surfaces flat ; those of the appendages in part are covered with strong 

 nodes. The plate overlying the costals, from which the bifurcation of the 

 ambulacra takes place, is large and nodose. It is succeeded by two rows of 

 transverse plates of irregular size, of which the larger ones are crowned by 

 nodes similar to those upon the orals, but more prominent, and with coarser 

 markings ; they are arranged transversely, like the plates bearing them. 

 The larger plates are so disposed that there is one at the base of each 

 arm, and by counting the nodes the number of the arms can be ascertained 

 from them as readily as from the brachials. Between every two nodal plates 

 are two or three smaller ones, which are flat, except for the general curva- 

 ture. Anus low down, facing laterally. Column large and long, rapidly 

 twisting ; the proximal joint circular, the succeeding ones turning abruptly 

 into elongate-elliptic — the long diameter twice the shorter one — and their 

 longitudinal thickness increasing as they recede from the calyx. Each joint 

 is twisted so that the long axes of its reverse faces make a considerable 

 angle with each other ; the other rim is beveled to an edge, from which 

 small tooth-like spines proceed outward. The articular ridge well defined, 

 and bordered at the sides by deep foss£e. Axial canal extremely small. 



Horizon and Locality. — Transition bed between the Upper Burlington 

 and Keokuk beds ; near Burlington and at Pleasant Grove, Iowa. Also in 

 the lower part of the Keokuk proper at Niota and Nauvoo, 111. 



Types In the collection of Wachsmuth and Springer. 



Eucladocrinus millebracliiatus var. immaturus W and Sp. 

 Plate LXXIII. Figs. 2, 3. 



There occur at Burlington in the same bed with Eucladocrinus miUe- 

 hrachiatus very much smaller specimens, which are so closely similar to that 

 species that they may represent its younger form ; but as no intermediate 

 stages have been discovered, and the gap is rather wide, we deem it advis- 

 able to place them at present as a variety under that species. The calyx in 

 these specimens, of which we obtained five examples in excellent preserva- 

 tion, is much shorter than wide, the dorsal cup saucer-shaped, the basal disk 



