676 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
one narrower and shorter than the corresponding plate of the other sides, 
the adjoining ones a little smaller. The succeeding plates are small, and 
form a tubular inflation which contains the anus. Of the column only the 
six proximal joints have been observed, all of which are circular. 
Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 
Type in the (Worthen) Illinois State collection, Springfield. 
Remarks. —'This and the succeeding species differ from all other Platy- 
crint known to us in having two costals. That this is not an abnormity, but 
a constant character in this species, is proved by the fact that we observed 
the same thing in four specimens and in all the rays. The species also 
departs from others in having but one interradial in contact with the radi- 
als, and the stem joints are apparently circular. If we were certain that 
the latter structure also occurred in P. eriensis, we should propose for the 
two species a new generic name. 
Platycrinus eriensis Hatt. 
1862. Hatz; 15th Rep. N. Y. State Cab. of Natural History, p. 119, Plate 1, Fig. 1. 
A small species, the dorsal cup scarcely more than 5 mm. in height, the 
arms three times as long. Basals anchylosed, curving gently upwards; the 
column facet comparatively large, bordered by a thickened rim. Radials a 
little wider than long, slightly spreading; the interradial sutures marked 
by a sharp line. The median line of the plates more prominent below the 
facets. Facets nearly one third the width of the plate. Costals two, the 
first quadrangular, the second pentangular, giving off two simple arms. Arm 
joints uniserial, as far as preserved, strong, subangular, thickened at their 
extremities, and supporting strong pinnules. Surface of plates granulose. 
The strong subangular joints of the arms, and the strong pinnules, are 
marked characters. 
Horizon and Locality. — In the shales of the Hamilton group, near Ham- 
burgh, Hrie Co., N. Y. 
Type supposed to be in the N. Y. State Cabinet of Natural History, 
Albany. 
Remarks. — To judge from the arm structure, the description was made 
from a very young specimen ; but it is interesting as having two costals like 
P. truncatulus. Our description is made after Hall. 
