HEXACRINID^. 777 



Dichocrinus dichotomus Hall. 



1859. Hall; Suppl. Geol. Rep. Iowa, p. 85 (diagram Plate 1, Kg. 5). 

 1881. W. and Sp. ; Revision, Palfeocr., Part II., p. 83. . 



According to Hall, the calyx is shallow cup-form, the basals occupying 

 one third its height. Eadials wider than long, the lower margin of the facet 

 slightly thickened. Costals extremely short and narrow, occupying scarcely 

 the fifth part of the width of the radials at the top. Arms dichotomizing 

 twice or oftener, uniserial in the lower portions ; composed of cuneate plate.?, 

 which gradually interlock upward. Surface of plates " punctate or marked 

 by slight rounded depressions, separated by narrow, elevated lines." 



Horizon and Locality. — Warsaw limestone, Warsaw, 111. 



Remarks. — This species was described from a crushed specimen in the 

 collection of the late Professor Worthen, from which the characters cannot 

 be satisfactorily ascertained. 



Dichocrinus Humburgi S. A. Miller. 



1891. S. A. MiLLEB; Geol Suit. Missouri, Bull. 4, p. 26, Plate 3, Figs. 9 and 10, and Adv. Sheets 

 17tli Rep. Geol. Surv. Indiana, p. 36, Plate 6, Pig. 38. 



Described from two specimens, which are only preserved to the second 

 palmar.?, and, according to Miller, " show considerable variation in size and 

 relative proportions," the radials of the one " only about one half longer 

 than wide," in the other " twice as long as wide." Basal cup a little less 

 than half the length of the calyx, obconical, truncated, and slightly concave 

 at the bottom, the column not filling the lower concavity, the re-entering 

 angles "hardly discernible on either side." Eadials expanding but little, 

 the facets occupying nearly the entire width of the plates. Costals " one," 

 thin and axillary. Distichals two. Arms twenty, uniserial so far as observed. 

 Anal plate a very little smaller than the radials, the upper end contracting. 

 Surface of plates smooth. 



Horizon and Locality. — Lower part of Warsaw limestone ; Boonville, Mo. 



Type in the collection of Mr. R. A. Blair, of Sedaha, Mo. 



EemarJcs. — The two specimens alluded to above not only differ in the 

 proportions of the plates, but also the re-entering angles meeting the basi- 

 radial suture, which in the one were said to be "hardly discernible," are in 

 the other, according to figure, unusually deep. The specimens evidently 



