MELOCRINID^. 329 



extremely large. Lower portions of the dorsal cup to the top of the costals 

 deeply concave, formmg 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 fiye shallow circular depressions occupying 

 two thirds of the basals, which probably lodged the quinquelocular or dorsal 

 organ. Eadials 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 mid Locality. — Upper Helderberg group ; near Jeffersonville, 

 Ind. 



Types in the Lyon collection. 



Remarhs. — Lyon describes this species as having 2X2" 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. 



42 



