— 
ACTINOCRINID &. 573 
part of the arm a zigzag outline. The upper parts of the arms have serrated 
sides, and are composed of two series of moderately long pieces. Regular 
interbrachials: 1, 2, 2; the anal plate followed by 2, 3, and 3 plates. Inter- 
distichals one, large. Ventral disk not visible in the specimens. 
Zorizon and Locality. — Lower Burlington limestone ; Burlington, Iowa. 
Types in the Museum of Comparative Zodlogy, and in the collection of 
Wachsmuth and Springer. 
- Actinocrinus tuberculosus W. and Sr. (mov. spec.). 
Plate LIT. Figs. Sa, 6, ¢. 
Of the type of A. tenwisculptus, but somewhat larger. Calyx a little 
higher than wide, the dorsal cup considerably shorter than the tegmen. 
Plates rather thin, the surface slightly convex, and ornamented by series 
of isolated nodes of various forms. The middle of the plates is occupied 
by a conical, sometimes rounded tubercle, which is surrounded by elon- 
vate nodes, directed one to each side, with their longer diameter toward 
the margins of the plates. From the middle of the second costals up- 
ward, sometimes even from the radials, the nodes are set close together 
in rows, and form high and sharp knife-like ridges with serrated edges, 
running to the bases of the free arms. 
Basals short, wider at the lower margin than at the upper, at the latter 
surrounded either by a thickened collar, or by a row of conspicuous nodes, 
of which there are generally three to each plate. Radials one third wider 
than long. First costals half the size of the radials, and quadrangular ; the 
second a little wider than the first, and heptangular. Distichals and pal- 
mars keel-shaped ; the former smaller than the costals, and once and a half 
as wide as long; the latter still smaller, and the angularity extending over 
the entire width of the plates. Arms three to each main division of the 
ray, or thirty in all, given off in the usual way; the proximal one from the 
outer sides of the distichals, the two others from the second palmars; they 
are long, flat, wider in the upper part than at their bases; the lateral mar- 
gins serrated. The four proximal arm plates are single, very high and cu- 
neate, a thorn-like projection extending out from their longer sides. The 
plates, as the arms become biserial, are short, and each one is covered with 
a transverse row of small pustules. Pinnules long, and to one half their 
