624 THE CRINOIDEA CAMEEATA OF KORTH AMERICA. 



Cactocrinus Arnold! W. and Sp. 

 Plate LYII. Figs. 4a, h. 



1887. Jdinocrinus AmoUi — ^. and Sp.; Geol. Rep. of Illinois (1890), p. 168, Plate 17, Pig- 10, and 



Fig. 3.* 

 1890. Actimcritms AritoJcU— S. A. Miiler; N. Auier. Geol. and Palffioiit., p. 217. 



Of medium size, witli long, slender spreading arms, and fan-like fringes of 

 pinnules. Form of calyx snbovate, gibbous below, spreading at the arm 

 bases. The surface of the plates indented with numerous shallow pits and 

 short grooves, whose rims, which are somewhat rounded off, connect with 

 each other from jjlate to plate, and on the same plate in intersecting wrin- 

 kles, all of which produces on the surface a somewhat irregular, cancellate 

 sculpturing. 



Basals short, without projecting rim ; the suture lines not grooved. 

 Radials large. First costals hexangular, half the size of the radials; the 

 second still smaller and heptangular. Distichals and palmars small. Nmnber 

 of arms variable, from four to six to the ray, — six being the exception; they 

 are heavier than in the preceding species, less crowded, and composed of 

 a double row of very short pieces, united longitudinally by waving sutures ; 

 they are ornamented on the back in the upper portions by two rows of 

 small nodes, one to each plate, in the lower portions by a more prominent 

 node on every sixth or seventh plate. .Pinnules long and in close contact, 

 the proximal eight or nine joints provided with conspicuous hooks, directed 

 upward, and forming with corresponding hooks of adjoining pinnules regular 

 rows, parallel to the arms. Kegular interbrachials six or more ; the first 

 equal in size to the first costals, the two of the second range to the second 

 costals, the upper ones considerably smaller. The anal side consists of about 

 eleven plates, the two upper ones resting between the arm bases, and in con- 

 tact with the ambulacrals. Ventral disk depressed liemispherical, occupying 

 less than one third the height of the calyx. It is composed of numerous 

 very small pieces, of irregular arrangement and nearly equal size, most of 

 them flat, with a few convex pieces scattered among them. Anal tube 

 small, slightly excentric, abruptly rising from the ventral disk. Column 

 composed of short joints of nearly imiform width. 



Horizon and Locality. — Same as last. 



* See correction under Cactocrinus onatissimus. 



