THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Pterotocrinus pyramidalis Lyon and Cass. 
Plate LXXIX. Figs. 4a, b. 
1859. lyon and Cassepay; Amer. Journ. Sci., Vol. XXIX., p. 69. 
1866. Ssumarp; Trans. St. Louis Acad. Sci., Vol. IL., p. 394. 
1881. W. and Sp.; Revision Paleocr., 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 
upper 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 
costals. 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 palmars 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 laterally, 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, coy- 
ered with longitudinal grooves for the reception 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 appendages, 
