ECHINODERMATA OF THE BRASSFIELD FORMATION 
19 
in place of three costals. In that case it is evident that the 
specimen here described has two radianal plates, the primitive 
radianal plate at the base of the right posterior arm and the 
secondary radianal plate w^edged in between the primitive radi- 
anal and the anal x plates. It is not known to what extent this 
secondary radianal plate will be found to be a constant feature 
in this species. 
Compared with the Brassfield species of Clidochirus described 
and figured by Springer, and also described in this paper, the 
crown of Clidochirus ulrichi is elliptical ovate rather than in- 
versely conical in form. The sides of the calyx are more di- 
vergent and the greatest width of the crown is near mid-length. 
All of the arm plates are relatively shorter and wider, especially 
in case of the costals and distichals. 
Myelodactylus (Eomyelodactylus) rotundatus 
sub-gen. et sp. nov. 
Plate I, fig. 8; plate II, fig. 3 
Fragment of column, coiled, about 115 mm. in length, broken 
off where the reversal of curvature begins, possibly within 25 
mm. of the base of the crown. The greater diameter of the stem, 
measured from the convex to the concave side of its curvature, 
equals 2.25 mm, throughout almost the entire length of the frag- 
ment, but at a distance of 5 mm. from the beginning of its re- 
versal in curvature this diameter diminishes rapidly and is 
reduced to 1.4 mm. at the broken end. It probably continued 
to diminish in size gradually toward the crown. The diameter 
at right angles to the one just discussed is a little less, thus pro- 
ducing a slightly elliptical cross-section. 
The length of the columnals varies. The first three columnals 
at the broken end, where reversal begins, occupy a length of 1.5 
mm.; the next three, 1.9 mm.; the next three, 2.0 mpi.; the next 
three, 2.3 mm. ; then the length of the columnals remains constant 
until a point opposite the broken end has been reached. Then 
the length diminishes to three columnals in 1.8 mm., remains 
