60 OWEN AND SHUMAKD'S FOSSIL CRINOIDEA. 



perforation corresponding to the columnar canal ; near the centre of the plate is the 

 commencement of three furrows, which proceed to the edges of the plate, dividing it 

 into three unequal parts. The surface is finely corrugated ; in some specimens 

 gathered into imbricating folds arranged in concentric lines, conformable to the 

 shape of the plate. 



The superior plates are five; broad, subhexagonal, and widen slightly from below 

 upwards. The excavations for the attachment of the arms are harp shaped, large, 

 and striated around the margin, with a deep angular notch at the summit. The 

 vertical diameter of the excavations is equal to about one-half of the length of the 

 plate. The surfaces of the plate are finely corrugated, sometimes gathered in 

 imbricating folds, finely striated, and disposed in lines parallel to the lateral and 

 inferior margins. The articular edges are striated, as are those of the basal plate; 

 and when connected together a deep angular gutter is formed at each of the sutures. 

 Arms. — We are only acquainted with the first joint of the arms of this species, 

 which remains attached in a single specimen. It is cuneiform, the upper edges being 

 bevelled so as to form two facets finely striated on the margin for the articulation of 

 two series of arm plates ; the external surface is corrugated. 



Column. — We have recognized merely a small fragment, consisting of the three 

 superior plates of this portion of the animal, which is preserved in the beautiful 

 specimen represented in Fig. 2, A. They are circular at the basal plate, but 

 become slightly elliptical as they recede from it; thin and of unequal diameter; each 

 joint is sharply carinated on the side and presents a serrated appearance, from the 

 elevated striae on the articular surface of one plate fitting into the intervals between 

 the striae on the other. 



Formation and Localities. — This exceedingly neat and elegant species is rather 

 rare, and occurs with the preceding in the sub-carboniferous strata at Burlington, 

 Iowa. We have not met with it at any other locality. 



Platycrinus Burlingtonensis. (New sp.) 

 • Pi. 7, fig. 5. 



Body cup-shaped, with a slightly pentagonal contour. 



Basal plate pentagonal, flattened, smooth, moderately thick, convex towards the 

 margins and depressed in the centre, with a circular facet for the articulation of the 

 supra-columnar joint. 



Superior plates five ; subhexagonal, smooth, slightly convex, and a little wider at 

 their superior than at their inferior margins. The breadth of the plates is about one 

 fourth greater than the height. The articulating surface for the attachment of the 

 arms is, in part, on the superior edge of the plate, and is somewhat reniform and 

 shallow ; in its longest diameter equal to about one-third the breadth of the plate. 



