744 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
in the typical section of the Camerata between the Melocrinidse and Bato- 
crinids. In both cases the group with pentagonal base, and in which the 
anal is unrepresented, is the earliest in geological sequence. 
The Hexacrinidz have not been discovered in any formation older than 
the Devonian; but there they occur abundantly in the Eifel limestones, 
from which twenty-four species have been described. They range through 
the different divisions of the Subcarboniferous, and are represented in the 
last member of that system, the Kaskaskia group, by twelve species. Beyond 
that they are not known; but we shall not be surprised to hear of a Hexa- 
crinoid being found in the Carboniferous. 
The Hexacrinidx are the only Camerata in which the arms are uniserial 
throughout the Devonian; they gradually become biserial in the Subcarbo- 
niferous, in the lower part of which all gradations, from uniserial to strictly 
biserial, are found together in the same genus. 
The family consists of six genera and eighty-five species: fifty-two from 
America, and thirty-three from Kurope. 
HEXACRINUS Avustry. 
1843. Austin; Monogr. Ree. and Foss. Crinoids, p. 48. 
1853. D»eKonincx and Lu Hon; Recher. Crin. Carb. Belg. p. 160. 
1855. FE. Rommer; Lethea Geog. (Auseg. 3), p. 244. 
1857. Jou. Mttrer; Neue Hchinod. Hifl. Kalk., p. 247. 
1857. Pricret; Traité de Paléont., Vol. IV., p. 332. 
1862. Dusarpin and Hurt; Hist. natur. des Zoophytes Echinod., p. 155. 
1867. ScuuttzE; Monogr. Hchinod. Eifl. Kalk., p..71. 
1879. W.and Sp.; Proceed. Acad. Nat. Sci. Phila., p. 252. 
1881. W. and Sp.; Revision Paleocr., II., p. 79. 
1881. W. and Sp.; Revision Paleocr., III., p. 116 (Proceed. Acad. Nat. Sci. Phila., p. 338). 
Syn. Platycrinus — Puitiips, 1841 (not 1836); Paleoz. Foss. Cornw., p. 28.. 
Syn. Platycrinus — Goipruss (in part); 1838, Nova Acta Ac. Leopold. XIX., p. 348. 
Syn. Platycrinus — Acassiz Gu part); 1835, Mem. Soc. Neuchat. L., p. 197. 
Syn. Platycrinus — Austin (in part); 1842, Ann. and Mag. Nat. Hist., Vol. X., p. 109. 
Syn. Platycrinus —C. ¥. Roemer ; 1843, Verstein des Harzgebirges, p. 9. 
Syn. Platycrinus —¥. A. Rormer; 1844, Rheinish. Uebergangsgebirge, p. 63. 
Syn. Platycrinus —F. A. Rormer; 1851, Verhandl. naturh. Vereins f. Rheinlande, p. 362. 
Syn. Platycrinus — Lyon; 1860, Trans. Amer. Philos. Soc., Vol. XIII, p. 459. 
The dorsal cup composed almost exclusively of basals and radiais; the 
latter enclosing a large anal plate. The basals consist of three subequal 
pieces, forming together a rather large, more or less deep cup or basin, 
hexagonal in outline. Radials large, subquadrangular; their superior faces 
excavated so as to form a facet for the reception of the costals; the limbs 
slightly truncated to receive the first row of interradials. The intervening 
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