190 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
posteriorly in most of the species of the Thysanocrinide. In the new genus 
Ldiocrinus, in which there is but one interbrachial plate to each of the five 
sides, there is no special anal plate, and the posterior interradial, which is 
larger and rests upon the basals, serves as the anal. 
_The family is confined to the Silurian, and is composed of six genera, 
with twenty-three species, of which sixteen are from America, and seven 
from the upper Silurian of England and Sweden. 
THYSANOCRINUS Hatt. 
1836. Dimerocrinus — Puruuies; Murchison’s Silur. Syst., p. 674, Plate 17, Figs. 4 and 5. 
1841. Dimerocrinus —Mé.LER; Monatsber. Berlin. Akad. d. Wissensch., p. 208. 
1850. Dimerocrinus — p’OrBIGNY; Prodrome I., p. 46. 
1852. Glyptaster —Hawt; Paleont. N. York, Vol. IL., p. 187. 
1852. Thysanocrinus — Har; Ibid. p. 190. 
1852. Dimerocrinus — pD’Orzieny; Cours ¢lément., Part IL., p. 142. 
1855. Dimerocrinus — Roemer; Lethwa Geognost. (Ausg. 3), p. 237. 
1857. | Thysanocrinus | __ Provpy; Traité de Paléont., Vol. IV., pp- 317 and 318, Plate C, Fig. 13. 
Dimerocrinus S 
1859. Dimerocrinus —Murcuison; Siluria (3d ed.), p. 535, Plate 13, Figs. 4 and 5. 
1862. | Thysanocrinus) _ tyssxamix and Huré; Hist. Natur. des Zoophytes, pp. 128 and 131. 
Dimerocrinus S 
1863. Glyptaster— Hatt; Trans. Albany Inst., Vol. IV., p. 202. 
1873. Dimerocrinus —SautER; Catal. Geol. Museum, Cambridge, p. 120. 
1878. Glyptaster — Hatt; 28th Rep. N. Y. State Mus. Nat. Hist. (ed. 2), pp. 181 and 183. 
1878. Hucrinus — Ance in; Iconogr. Crin. Suecie, p. 24. 
Thysanocrinus ) 
1879 ee — ZitreL; Handb. d. Paleont., Vol. I., pp. 368 and 375. 
Eucrinus 
(peewee ) —W. and Sp.; Revision Paleocr., Part II., pp. 193 to 199. Also ibid., Part 
cet Dimerocrinus ( IIL., p. 101. 
vat eee ) 
Thysanocrinus (syn. of Dimerocrinus). 
\ Glyptaster ) 
1889. Eucrinus —S. A. Mitten; N. Am. Geol. and Paleontology. 
| Thysanocrinus \ 
Syn. Dimerocrinus Pures. 
Syn. Glyptaster Hau. 
Syn. Lucrinus ANGELIN. 
Calyx subglobose, urn or bell-shaped; the rays marked by a more or less 
conspicuous ridge; the general surface of the plates smooth or variously 
ornamented. Infrabasals five, small, barely protruding beyond the column, 
or entirely hidden by it. Basals five, four of them equal, angular above ; the 
fifth truncated, and supporting a large anal plate. Radials considerably 
larger than the costals, their lower sides distinctly angular, the lateral faces 
comparatively short. Costals two. Arms ten or twenty, rather strong and 
