308 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



AUocrinus Benedicti S. A. Miller. 

 Plate XXIV. Figs. 8a, h. 



1891. S. A. Miller ; Adv. Sheets 17tli Rep. Geol. Surv. Indiana, p. 37, Plate 7, Tig. 1. 



Closely resembling the preceding species, but the -dorsal cnp 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 Sp. 



1881. W. and Sp. ; Revision Palseocr , Part II., p. 104 (Proceed. Aoad. Nat. Sci. Pliila., p. 278). 

 Syn. Actimcritius (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. Eadials 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. Eep. Illinois, Yol. VIIL, p. 

 95, Plate 14, Fig. 1), has infrabasals, and is a totally different thing. 



Remarks. — The name Cefitroemius was previously proposed by the 



