308 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Allocrinus Benedicti S. A. Mrter. 
Plate XXIV. Figs. Sa, b. 
1891. S. A. Minter; Adv. Sheets 17th Rep. Geol. Surv. Indiana, p. 37, Plate 7, Fig. 1. 
Closely resembling the preceding species, but the dorsal cup a little 
smaller and less sharply angular, the plates generally more convex, and 
the arms not quite so stout. Dorsal cup bowl-shaped, a third wider than 
high, the lower end distinctly truncate, the sides convex, the plates elevated 
and more or less nodose. 
Basals forming an equilateral pentagonal disk, which has twice the diam- 
eter of the column, and occupies the bottom of a shallow concavity ; inter- 
basal sutures indistinct. Radials large, curving gradually upwards, their 
upper ends at right angles to the lower. Both costals together of about 
the size of the radials, wider than long, the sides decidedly beveled and 
forming a deep groove toward the interbrachials. First costals quadrangu- 
lar, the second pentangular. Distichals one in the calyx, the others free. 
Arms ten, so far as observed, moderately heavy ; their plates quadrangular. 
Interbrachials one, very large, elongate, and highly convex in the middle, 
beveled around the margins. Structure of ventral disk unknown. 
Horizon and Locality. — Niagara group; St. Paul, Ind. 
CENTROCRINUS W. and Sr. 
1881. W. and Sp.; Revision Paleocr, Part IT., p. 104 (Proceed. Acad. Nat. Sci. Phila., p. 278). 
Syn. Actinocrinus (in part) Lyon; 1869, Trans. Amer. Philos. Soc., p. 453. 
Dorsal cup elongate, plates smooth. Basals represented by a large 
pentagonal disk, showing no traces of suture lines. Radials unusually 
large, followed by two costals, which are proportionally very small. Dis- 
tichals still smaller, taking the form of arm plates. Arm openings large, 
directed outward. First interbrachial plates large, followed by two smaller 
pieces. All other parts of the calyx unknown. Column very small. 
Distribution. — Represented, so far as known, by a single species from 
the Hamilton group of America. Centrocrinus tennesseensis Worthen, from 
the Niagara group of Western Tennessee (Geol. Rep. Illinois, Vol. VIIL, p. 
95, Plate 14, Fig. 1), has infrabasals, and is a totally different thing. 
Remarks. — The name Centrocrinus was previously proposed by the 
