620 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Caetocrinus fossatus s. A. Millee. 

 Plate LV. Fig. n. 



1892. Acimocrinus fossatus — S. A. Milleb; Adr. 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. Eadials 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, 3, and 2 smaller pieces. Ventral di.sk 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. 



Horizon and Locality. — Lower Burlington limestone ; Sedalia, Mo. 



Type in the collection of S. A. Miller. 



Remarks. — Approaching C. ccelatus 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 uniforrri size, and 

 each one is extended into a long, heavy spine ; while those of G. ccelatus 

 vary considerably in size, the principal ones being slightly nodose, and the 

 others almost flat. 



