HEXACRINIDZ. 753 
DICHOCRINUS Munster. 
1838. Miunstrr; Beitr. zur Petrefactenkunde, I., p. 2. 
1843. Austin; Monogr. Rec. and Foss. Crinoids, p. 45. 
1850. D’Orsieny; Prodr. de*Paléont., L., p. 156. 
1852. Owxn and Saumarp; Geol. Rep. Iowa, Wisc., and Minnesota, p. 589. 
1853. Der Konrncx and Le Hon; Rech. Crin. Carb. Belg., p. 146. 
1857. Pictnt; Traité de Paléont., Vol. IV., p. 333. 
1860. Mzrx and WortHen; Proceed. Acad. Nat. Sci. Phila., p. 381. 
1860. Hatt; Suppl. Geol. Rep. Iowa, p. 83. 
1860. Cassrpay and Lyon (in part); Proceed. Acad. Arts and Sci., Vol. V., p. 16. 
1861. Harz; Bost. Journ. Nat. Hist., Vol. XII., p. 288. 
1862... Dusarpin and Hurt; Hist. naturelle des Zoophytes Echin., p. 155. 
1862. Wuuttz; Proceed. Bost. Journ. Nat. Hist., Vol. IX., p. 19. 
1866. Merx and WortHen; Geol. Rep. Illinois, Vol. IL, pp. 167 and 2638. 
1879. Zirrun; Handb. der Palaeontologie, Vol. I., p. 365. 
1881. W. and Se.; Revision Paleocr., Part II., p. 81. 
1882. Dx Lorton; Paléont. Frangaise, Crinoides, Part I., p. 33. 
1883. Wortuun; Geol. Rep. Illinois, Vol. VII., p. 313. 
1885. W. and Sp.; Revision Paleocr., Part III., p. 119 (Proceed. Acad. Nat. Sci. Phila., p. 341). 
1890. W. and Sp.; Geol. Rep. Illinois, Vol. VIII, p. 190. 
1890. §. A. Minter; North Amer. Geology and Paleontology, p. 239. 
Not Hall 1858; Geol. Rep. Iowa, Vol. L., Part IL., pp. 654 and 689; nor Shumard 1857; Trans. 
St. Louis Acad. Nat. Hist., Vol. I., p. 5. 
Syn. Platycrinus (in part) — Puruiies; Geol. of Yorkshire, Vol. I., Plate 3, Figs. 24 and 26. 
Syn. Cotyledonocrinus — Cass. and Lyon. 1860, Proc. Am. Ac. Arts and Sci., V., p. 26. 
Calyx oblong, conical to almost cylindrical. The dorsal cup consists 
almost exclusively of basals, radials, and a large anal plate. The costals and 
distichals, although laterally connected by interbrachials, and taking part in 
the composition of the calyx, more or less, retain the form of arm plates. 
Plates delicate; their surfaces smooth, or covered with longitudinal striae or 
rows of small tubercles. Basals two, the suture line running from the anal 
plate to the anterior radial. They form together a deep obconical or rounded 
cup, which in height often equals the length of the radials. Radials large, 
subquadrangular, except the anterior one, which is pentangular; their upper 
faces excavated for the reception of the brachials. Costals two, very short 
and narrow. In some species the axillary costals support the arms, in others 
those of the distichals or palmars, and the first and second plate of each 
order are united by syzygy. Arms thin, either uniserial or biserial, some- 
times pendent. Pinnules unusually long and rather stout. Interbrachials 
three, arranged transversely ; they rest upon the upper faces of the radials 
and are succeeded by a number of interambulacral pieces, The covering 
plates of the ambulacra generally exposed and forming continuous rows. 
Anal plate frequently a little smaller than the radials, pentangular, narrower 
at the upper end than at the lower. Anus excentric, placed within a wart- 
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