556 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



others pass out to the costals and first interbrachials, and from one to three 

 to the other plates; but only those of the middle series are continuous, the 

 two at the sides which form the inner triangles, when present at all, being 

 interrupted and less distinct. 



Basals large, forming a broad cup, with rapidly- expanding sides; the 

 lower margins projecting over the top of the column, somewhat thickened, 

 and slightly notched at the sutures ; the axial canal sharply pentangular. 

 Radials large, longer than wide, the sloping upper faces much smaller than 

 the lateral ones. First costals nearly as long as wide, scarcely half the size 

 of the radials, and hexangular ; the second costals from one third to one 

 half smaller than the first. Distichals small, twice as wide as long, axil- 

 lary ; their sloping outer faces support an arm, which becomes free from the 

 second plate, the inner faces two palmars (rarely one or three), of which the 

 upper is axillary and gives off a single arm at one side, at the other post- 

 palmars and two arms. Arms forty, of moderate size, simple through- 

 out, slightly tapering, and somewhat flattened toward the extremities; the 

 plates transversely angular. Pinnules long, their two or three proximal 

 joints covered with small hooks. First interbrachials a little larger than the 

 first costals, supporting two plates, followed by four, of which the two lower 

 are in part interambulacral, and the upper ones touch the orals. Occasion- 

 ally there are two additional plates between those of the .'^econd and third 

 rows. Anal interradius very wide ; the anal plate succeeded by two plates 

 in the first, three in the second, and five in the third row ; those of the 

 latter, which occupy the equatorial zone, are followed by irregular pieces in 

 the tegmen. Teginen very short ; the plates moderately large, slightly 

 convex, their surfaces rugose. Orals comparativelj' small, especially the 

 posterior one, which is smaller than the others, and is placed at the side of 

 the anal tube. Tube nearly central, long, heavy throughout, and frequently 

 curving; the plates sharply nodose and transversely arranged. The ambu- 

 lacral plates, covering the calj^cine extensions, decrease in size outward, 

 and are immovable ; those of the first and second orders consist of large 

 single pieces, but those of the higher orders of two rows of plates. Col- 

 umn proportionally small, composed in the upper part of thicker and 

 thinner joints, the former widest at the top; but at 50mm. from the calyx 

 all joints have nearly the same dimensions. 



JETorkon and locality. — Upper Burlington limestone, Burlington, Iowa, 

 Quincy, Ills., Hannibal, Mo., and other places. 



