798 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



Pterotocrinus pyramidalis Lton and Cass. 

 Plate LXXIX. Figs. 4a, h. 



1859. Lyon and Casseday ; Amer. Journ. Sci., Tol. XXIX., p. 69. 

 1866. Shumaed ; Trans. St. Louis Acad. Sci., Vol. II., p. 39i. 

 1881. W. and Sp. ; Revision Pa]a;ocr., Part II., p. 91. 



A little larger than the preceding species. Dorsal cup saucer-shaped, 

 broadly truncate at the lower end ; the sides rapidly spreading, especially 

 from the top of the radials upward, bringing the upper portions into a nearly 

 horizontal position. Plates thick and without ornamentation. 



Basal cup very short, a little projecting laterally ; oblong, the longer 

 diameter transverse to the suture ; the upper margin distinctly notched for 

 the reception of the anal plate, and somewhat less toward the anterior radial. 

 Radials subquadrangular, rapidly spreading, fully one third wider at the 

 iipper end than at the lower ; the median portions of the upper faces slightly 

 excavated for the reception of the distichals and the middle part for the 

 costala. Costals very small, trigonal. Distichals smaller than the palmars. 

 The first and second palmars larger than the third, and forming part of the 

 calyx ; the third partly free. The first palmar.s of the two outer divisions of 

 the ray are pentangular, and rest with their lower faces against the sloping 

 upper faces of the distichals, with one of their lateral faces upon the radials, 

 and the other against the first palmar of the inner division. The second 

 palmars are supported by the first, and rest at one side against the second 

 and third of the two inner divisions, and at the opposite side against the 

 palmars of adjacent rays. The three palmars of the two inner divisions thus 

 meet laterallj^, and interlock with those of the outer divisions. Arms four to 

 the ray, short, biserial above the third palmar. Anal plate lozenge-shaped, 

 large, its upper end inflected and not seen in a side view. Ventral disk, the 

 appendages removed,, pyramidal, the sides flattened or slightly concave, cov- 

 ered with longitudinal grooves for the recepition of the arms. The interam- 

 bulacrals at the four regular sides consist of three plates in two rows ; they 

 are of about equal size, and all longer than wide ; the first, which is flanked 

 by two secondary radial dome plates, is hexagonal, the two succeeding ones 

 pentagonal and in contact laterally with those of adjacent sides. The latter 

 plates, as also the orals, are bevelled off at one side to a third of their width, 

 and the depressions thereby produced form the sockets for the apipendages, 



