620 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Cactocrinus fossatus S. A. Mizzuzr. 
Plate LV. Fig. 12. 
1892. <Actinocrinus fossatus—S. A. Minunr; Adv. Sheets 18th Rep. Geol. Surv. Indiana, p. 40, Plate 6, 
Figs. 11 and 12. 
Calyx moderately large, subovoid. Dorsal cup truncated at the base, the 
sides a little convex; height and width as 3 to 4. Plates rather delicate 
and deeply sculptured. The middle of the plates occupied by a sharp 
angular node, from which angular ridges, one to each side, pass out to 
the margins, where they meet with those of adjoining plates. Angles of 
the plates depressed, the suture lines rather indistinct. | 
Base short, projecting laterally, and forming a rim, which expands be- 
yond the column and the lower face of the radials, and is slightly notched at 
the interbasal sutures. Columnar cavity rather shallow. Radials wider than 
long. First costals about two thirds the size of the radials, hexagonal; sec- 
ond costals a little larger than the first, pentagonal or hexagonal. Dis- 
tichals, palmars, and post-palmars all axillary, the post-palmars supporting 
the free arms, of which there are eight to the ray. Ambulacral openings 
almost equidistant, the interspaces between those of adjoining rays a very 
little the widest. Interradial areas arched by the post-palmars; those of the 
regular sides consisting of five plates: 1, 2,2. Anal plate as large as the 
radials ; followed by 2, 8, and 2 smaller pieces. Ventral disk highly convex, 
only one fourth shorter than the cup; covered with large plates, and each 
of them prolonged into a heavy spine. Orals pushed to the anterior. Anal 
tube almost central. 
Florizon and Locality. — Lower Burlington limestone ; Sedalia, Mo. 
Type in the collection of S. A. Miller. 
femarks. — Approaching C. celatus in the form and ornamentation of the 
dorsal cup, and also in the number of arms; but differing in the form and 
construction of the ventral disk, which in the latter is higher, and gradually 
tapers to the anal tube, instead of being highly convex as in this species. 
In C. fossatus the disk plates are less numerous, almost of uniform size, and 
each one is extended into a long, heavy spine; while those of C. celatus 
vary considerably in size, the principal ones being slightly nodose, and the 
others almost flat. 
= > eae 
