560 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



sides expanding regularly from the base to the top of the costals, the higher 

 brachials horizontal. Ventral disk depressed convex, occupying about one 

 third the height of the calyx. Surfaces of plates somewhat variable, but, 

 as a rule, the radials and anal plate strongly nodose, the nodes transversely 

 arranged, covering the whole surface of the jjlates, and extending obliquely 

 outward. From the sides of these nodes indistinct ridges or angularities 

 pass out to the costals, giving to the section of the cup an obscurely pen- 

 tangular outline ; similar ridges proceed to the basals. The first inter- 

 brachials are marked with very prominent rounded tubercles, rising 

 abruptly at the middle of the plates, while the higher interbrachials are 

 nearly flat. 



Base short, deeply grooved at the sutures, and notched at the lower 

 margins, presenting three well marked lobes, which, hanging downward, 

 enclose the proximal stem joints. Eadials nearly as large as both costals 

 together, and as wide as long. First costals hexangular; the second wider 

 than long, and generally smaller than the first. Succeeding brachials small, 

 exteriorly rounded, with deep longitudinal grooves at the sides. Distichals 

 all axillarj^, their sloping outer fiices giving off an arm, the inner ones of both 

 ray divisions two palmars, and these again an arm from the one side, and 

 t-\vo post-palmars from the other, of which the axillary supports two arms. 

 Arms forty (not twenty as supposed by Hall, nor thii'ty as given by Meek 

 and Worthen) ; long, rounded, not branching in their free state, and not 

 tapering at the extremities. Interbrachial spaces slightly flattened; they 

 consist at the regular sides of 1, 2, and 4 plates, the latter row on a level 

 with the arm openings, and at the anal side of 2, 3, and 5 pieces. Plates 

 of the tegmen of medium size ; the orals, which are slightly' the largest and 

 not in contact with each other, placed at some distance from the summit. 

 Ambulacral plates of first and second orders represented by large single 

 plates, those of the higher orders by rows of small covering pieces. Anal 

 tube central, and of moderate size. 



Horizon and Locality. — Upper Burlington limestone, Burlington, Iowa, 

 and at the same horizon in Missouri and Illinois. 



Tijpes in the (Worthen) Illinois State collection, Springfield. 



