MELOCRINID&. 329 
extremely large. Lower portions of the dorsal cup to the top of the costals 
deeply concave, forming a large inverted cup, which extends deeply into 
the cavity of the calyx; the succeeding plates spreading almost horizontally 
with a slight upward curvature. The entire surface covered with somewhat 
flattened ridges passing from near the centre of the plates to their sides, 
where they meet the ridges of adjoining plates. There are from two to four 
ridges to each side, but two of them are frequently united in the specimens, 
so as to form one larger ridge with a broader surface. 
Basals closely united, forming a small inverted cone, which occupies the 
bottom of the dorsal cavity and is completely hidden by the column. The 
inner or ventral surface of the basals is convex, decidedly wider than the 
outer or dorsal surface, and marked by five well defined angular ridges, 
radial in position, from which small protuberances pass out and enter the 
axial canal, producing the pentalobate outline. Between these ridges and 
around the axial canal, there are five shallow circular depressions occupying 
two thirds of the basals, which probably lodged the quinquelocular or dorsal 
organ. Radials large, somewhat variable in size, about as wide as long; the 
lower faces wider than the upper; the upper sloping faces less than one half 
the length of the lower ones. Costals pentangular, very much smaller than 
the radials, sometimes barely one third their size. First interbrachial rising 
to the top of the costals, the two of the second row elongate and but little 
smaller; they are followed by other rows, but their arrangement, as well 
as that of the higher brachials, cannot be accurately determined from the 
specimens. 
Horizon and Locality. — Upper Helderberg group; near Jeffersonville, 
Ind. 
Types in the Lyon collection. 
Remarks. — Lyon describes this species as having 2 X 2 “secondary 
radials,” and several more “ orders of radials” above, each order represented 
by two plates, and he mentions seven to eight “interradials” and two “ in- 
teraxillaries.” He also suggested from small detached pieces, which may 
possibly belong to a very different form, that this species had from eighty to 
one hundred arms; all of which has yet to be confirmed by more perfect 
specimens. 
