676 THE CRINOIDEA CAMERATA OF NORTH AilEEICA. 



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. 



Tt/23& in the (Worthen) Illinois State collection, Springfield. 



Remarks. — This and the succeeding species differ from all other Platy- 

 crini 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 Hall. 



1862. Hall; IStli Eep. N. Y. State Cab. of Natural History, p. 119, Plate 1, Tig. 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, Erie Co., N. Y. 



Ttjfe, 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. ti'uncatulus. Our description is made after Hall. 



