■^ 



RHODOCRINID^. 253 



to adjoining basals, the latter forming upon the surface a well defined five- 

 rayed star, whose salient angles alternate with the angles of the basal 

 concavity. 



Infrabasals small, and almost completely covered by the upper joint of 

 the column. Basals large, elongate ; spread out horizontally, except their 

 lower ends, which form the sides of the funnel-shaped pit. Kadials large, 

 their lower faces sharply angular. Costals smaller than the radials ; the 

 second considerably smaller than the first. Distichals free from the second 

 plate ; very short. Arm structure unknown. Interbrachials : 1, 2, 3, 2, 1, 

 with variations of three plates in the second, and two to four in the third 

 ranges • the first plate large, being next to the basals the largest plate of the 

 calyx ; the plates of the second row considerably smaller, especially when 

 there are more than two plates in that row. The supplementary interradials 

 are less frequently represented than in the preceding species, and rarely by 

 four plates to the interray ; but there is scarcely a specimen in which there 

 is not at least one of them introduced at one side. The plates of the third 

 row are placed between the arm bases ; the succeeding ones form part of the 

 ventral disk. The anal side is wider and the plates more numerous -, there 

 being three or four in the second row, and four or more in the succeeding 

 ones. Yentral disk almost as high as the dorsal cup; composed of rather 

 large convex plates of nearly uniform size. Orals cannot be identified, the 

 whole ventral pavement consisting of the same kind of irregularly arranged 

 plates. Anus nearly central, extended into a strong tube. Column near 

 the calyx apparently slightly pentangular ; central canal very large and 

 pentalobate. 



Horizon and Locality. — Trenton group \ near Knoxville, Tenn. 



Tyjpes in the collection of Wachsmuth and Springer. 



Remarks. — This species is distinguished from the preceding one by the 

 different form of the calyx, the peculiar style of ornamentation, and by the 

 irregularity in the distribution of supplementary pieces in the interradial 

 series. 



ARCH^OCRINUS W. and Sp. 



1881. W. and Sp. ; Revision Palseocr., Part II., p. 189 ; also Proceed. Acad. Nat. Sci. Phila., p. 363. 



1885. W. and Sp. ; Revision Palseocr., Part III., p. 96 ; Proceed. Acad. Nat. Sci. Phila., p. 318. 



1883. S. A. Miller; Journ. Cincin. Soc. Nat. Hist., Vol. VI., p. 217. 



1889. S. A. Miller; N. Amer. Geol. and Pal^ont., p. 224. 



Calyx large, obconical or subovate ; plates smooth or variously orna- 

 mented ', those in a radial direction marked along their median line by 



