264 SMITHSONIAN INSTITUTION 



ICHTHYOCRINUS Conrad 

 Plates XXXII-XXXVI 



Ichthyocrinus Conrad, Jour. Acad. Nat. Sci. Philadelphia, VIII, 1842, p. 279. — D'Orbigny, Prodr. Pal. 

 Stratigraphique, I, 1849, p. 46; Cours Elem. Pal. et Geol. Strat, II, 1851, p. 144. — Hall, Nat. Hist. 

 New York, Pal. II, 1852, p. 195; Geol. Iowa, I, pt. 2, 1858, p. 557.— McCoy, Syn. Brit. Pal. Fossils, 

 1854, p. 54. — Roemer in Bronn, Lethaea Geognostica, I, 1852-54, p. 237. — Pictet, Traite Paleontologie, 

 IV, 1857, p. 319. — Bronn, Klassen Ord. Thier-Reichs, II, i860, p. 231. — Quenstedt, Handb. Petre- 

 faktenkunde, 1867, p. 737; Petref. Deutschlands, IV, 1876, p. 515. — Beyrich, Monatsber. Akad. Wiss. 

 Berlin, 1871, p. 42 (Trans, in Ann. and Mag. Nat. Hist., (4) VII, p. 403). Salter, Cat. Cambrian 

 and Silurian Fossils, 1873, p. 126. — Angelin, Icon. Crin. Sueciae, 1878, p. 13. — Wachsmuth and 

 Springer, Proc. Acad. Nat. 'Sci. Philadelphia, 1878, p. 252 ; ibid., 1888, p. 353 ; 1890, p. 387 ; Revision 

 Palaeocrinoidea, pt. 1, 1879, p. 33; ibid., pt. 3, 1886, p. 143. — Von Zittel, Handbuch Palaeontologie, 

 I, 1879, p. 355 ; Grundziige Palaeontologie, 1895, p. 138. — Miller, N. A. Geol. and Pal., 1889, p. 256. — 

 Zittel- Eastman, Textbook Palaeontology, 1896, p. 163 (2d Ed., 1913, p. 204). — Bather, Proc. Zool. 

 Soc. London, 1896, p. 998; Natural Science, XII, 1898, p. 341; Ann. and Mag. Nat. Hist., (7) VI, 

 1900, p. 112; Treatise on Zoology (Lankester), pt. 3, 1900, p. 188. — Weller, Bull. IV, Chicago Acad. 

 Sci., I, 1900, p. 145. — Springer, Amer. Geologist, XXX, 1902, p. 94; Jour. Geology, XIV, 1906, p. 475. 



4g^ 



Fig. 36. Ichthyocrinus 



Ichthyocrinidae with rays in contact all around. Crown elongate, expand- 

 ing from radials up. Infrabasals entirely within ring of basals, sometimes 

 resorbed. Posterior basal not differentiated. Radianal in primitive position 

 under right posterior radial, touching right anterior radial; smaller than, and 

 of similar form to, other radials. No anal or interbrachial plates. Primibrachs 

 two. Rays widening from radials up. Arms dichotomous, interlocking to at 

 least the second subdivision, closely abutting above that ; they are mere continua- 

 tions of the ray divisions without line of demarcation. Column proximally 

 enlarging, usually to the diameter of the base. 



Genotype. Ichthyocrinus laevis Conrad. 



Distribution. Silurian and Devonian; Europe and North America. 



The genus Ichthyocrinus is a typical and perhaps the most characteristic representative 

 of the Crinoidea Flexibilia, giving the name to the group in which their peculiar characters 



