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ACTINOCRINID &. 613 
of nearly equal size, and as large as the first costals. Occasionally there is 
another small elongate plate between the arm bases, but more frequently 
this is absent, and the palmars are in contact laterally. Anal interradius 
formed of six to seven plates; the upper one very elongate, resting between 
the palmars. Interdistichals one. Ventral disk covered by numerous small 
and extremely irregular pieces, which enclose somewhat larger spinous 
plates, probably representing the orals, and radial dome plates of a first, 
second, and third order. Column large; axial canal very wide and obtusely 
pentangular; the joints are long, the third from the calyx wider and longer 
than the surrounding ones, in some specimens almost twice as wide, and 
having a knife-like edge. 
Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa. 
Type in the University Museum at Ann Arbor, Mich. 
fiemarks.— This species is well characterized by the form of the calyx, 
and by the smooth and heavy arms without nodes or spines. It was described 
by Hall as having six arms in each ray, which is certainly incorrect. We 
have examined seven specimens, in all of which the antero-lateral rays have 
but five arms, while the others have six. 
Cactocrinus obesus Kzyzs (MS.). 
Plate LV. Figs. 9a, b. 
A large species of the type of @. clarus, but more elongate, much more 
nodose, and having but four arms to the ray. Calyx once and a half as wide 
as high, broadly and sharply truncated at the base; the plates thick and 
heavy. Dorsal cup gradually expanding to the top of the distichals, then 
bending abruptly outward. The plates of the dorsal cup extremely heavy, 
highly elevated, and produced into rather sharp, round nodes, especially the 
radials, which are decidedly more prominent than the succeeding plates; the 
suture lines traversed by short, obscure ridges. Ventral disk high-conical, 
as high as the dorsal cup, its sides but very slightly convex; orals and first 
radial dome plates wedge-shaped, and produced into very long, sharp, broadly 
transverse tubercles, which stand out conspicuously (5 to 7 mm.) from the 
tegmen. 
Basal cup short but wide, much wider than the column; sub-cylindrical ; 
the lower end abruptly truncated, forming a sharply angular edge at the 
bottom; the suture lines not grooved. Radials a little wider than long, 
