794 THE CEINOIDEA CAMEEATA OF NORTH AMERICA. 



last surviving genus of the Hexacrinidse ; and it is most interesting to find 

 here again emphasized the truth which Palseontology teaches us by so many- 

 examples, that extravagance of form and rank development in any group is 

 the signal for its speedy extinction. 



Pterotocrinus capitalis (Lyon). 

 Plate LXXIX. Figs. 6a, h. 



1857. Asterocrinm capitalis — Lyon ; Geol. Rep. Kentucky, Vol. III., p. 473, Plate 3, Figs. 1, \a-k. 

 1859. Pterotocrinus capitalis — Lton aud Casseday ; Amer. Jouvn. Sci., Vol. XXIX., p. 68. 

 1881. Pterotocrinus capitalis — W, and Sp. ; Revision Paloeocr., Part II., p. 91. 



Crown as viewed from above irregularly star-shaped, in profile resembling 

 the form of a Corinthian capital. Dorsal cup about as wide as high, the 

 plates heavy and without ornamentation. 



Basals proportionally larger than in any other known species of the 

 genus, forming a rather deep basin, almost as large as the remaining portions 

 of the dorsal cup together; the sides rounded, contracting at the upper end, 

 and somewhat flattened at the bottom ; the median portions slightly concave, 

 with a deep pit in the centre, completely filled by the column. The upper 

 margin of the basal cup is indented for the reception of the radials, and 

 deeply notched for the anal plate. The latter extends to the full height of 

 the radials, but is considerably narrower ; it is trapezoidal, the iipper angle 

 being acute, the lower one obtuse. Radials very short, their width almost 

 four times their height ; the lower face convex, the upper excavated by the 

 radial facets. Costals larger than usual in the genus, wider than long, trian- 

 gular; the lateral faces a little concave. Distichals twice the size of the 

 costals, wider than long, the upper angles obtuse. Fixed palmars 1 X 4, in 

 contact laterally ; the two outer ones resting with one of their lower faces 

 upon the radials, with the other against the distichals ; the two inner plates 

 of the rays supported exclusively by the distichals ; all succeeding brachials 

 free. Arms four to the ray, short, rather strong, tapering to the tips, and 

 incurving. They are biserial from the second plate, and the two series are 

 united by a zigzag suture. Structure of the greater part of the ventral disk 

 not known. The orals, of which portions are exposed, are elongate and 

 almost — some of them completely — separated by the wing-like appendages. 

 The latter, as viewed from the side, are elongate subtrigonal, with rounded 

 outer angles ; they are massive, deep, and flattened at the sides, thicker at 



