ACTINOCRINID^. 615 



and costals of nearly the same size, and all a little wider than long ; the 

 distichals of the .same form, and but slightly smaller; the palmars about half 

 the size of the distichals. The outer palmars of each ray support an arm, 

 the inner ones two small post-palmars and two arms. Arms crowded, long, 

 rather heavy throughout, rounded on the back, their upper parts incurving, 

 their proximal ends bending almost horizontally outward. Interbrachials 

 five at the regular sides : 1, 2, 2 ; and there are 2, 3, and 2 above the anal 

 plate. Some specimens have an additional narrow piece wedged in between 

 the palmars. Interdistichals one. Ventral disk conical, slightly expanding 

 near the arm bases, then rising evenly, and passing insensibly into the anal 

 tube. The plates close to the arm regions are very small and almost flat, 

 higher up larger and nodose plates are interposed between smaller ones, and 

 at the foot of the anal tube ah the plates are large and sharply nodose. 

 Anal tube long, extending beyond the arms ; composed of rather large, 

 convex pieces, which decrease in size with the tube. 

 Horizon and Locality. — Same as last. 



Cactocrinus sexarmatus (Hall). 

 Plate LV. Figs. 10 and 11. 



1860. Actimcrinas sexarmatus — Hall; Suppl, Geol. Eep. Iowa, p. 21 (not Bull. I., N. Y. State Mus. 



Nat, Hist., 1872, Plate 3^, Tig. 26 = Cactocrinus extensiis W. and Sp.). 

 1881. Aeiinocrinus sexarmatus — W. and Sp. ; Revision Palaeocv., Part II., p. 145. 



Eeadily distinguished from the other species of this genus by the form of 

 the calyx, which is biturbinate ; the arm bases are not spreading, and the 

 arm openings directed obliquely upwards. Dorsal cup deejDly bowl-shaped, 

 truncate at the base, the sides slightly convex below, and straight above. 

 Plates but little elevated, their middle portions flat and perfectly smooth; 

 but they are connected with adjoining pieces by short, prominent ridges, 

 which form deep, trigonal pits at the angles of the plates. 



Basals trilobate, short but wide, and somewhat spreading outward; the 

 lower surface a little excavated for the reception of the column, which occu- 

 pies about half its diameter. Eadials very large, nearly as long as wide, 

 and nearly as large as both costals together. First costals hexagonal, one 

 fourth wider than long; the second about the same size as the first, but 

 heptagonal. Distichals, palmars, and post-palmars rapidly decreasing in size 

 upward, the first post-palmars elongate and semi-free. Arms six to the ray, 

 the outer palmars of the rays being axillary. The structure of the arms is 



