ORDER II CRINOIDEA—CAMERATA 145 
Xenocrinus, 8. A. Miller. JB obsolete; 6 four; column quadrangular. 
Otherwise resembling Feteocrinus. Ordovician ; North America. 
Family 6. Thysanocrinidae. Wachsmuth and Springer. 
(Glyptocrinidae, pp. Zittel ; Glyptasteridae, Angelin.) 
Base dicyclic. Radials laterally in contact, except at the posterior side, where they 
are separated by an anal plate. This is followed by several rows of interradials, 
between which additional anals are interposed, Ordovician and Silurian. 
[ Thysanocrinidae was substituted by W. and Sp. as a family name, on dis- 
covering the identity between Glyptaster, Dimerocrinus, Hucrinus, and Thysano- 
crinus. The last-named genus is entitled to priority, from being the first to 
have received a tolerably accurate description. Gyptocrinus, Hall, and Stelidio- 
crinus, Ang., are removed to the Melocrinidae. | 
Thysanocrinus, Hall (Glyptaster, Hall ; Dimerocrinus, Phill. ; Lucrinus, Ang.) 
Calyx deep. JA followed by three plates. Arms ten to twenty, biserial. 
Silurian (Niagara Group) ; North America, England, Gottland. 
Hyptiocrinus, W. and Sp. Dorsal cup saucer-shaped, almost flat ; the larger 
plates of the tegmen spiniferous. Arms pendent. Niagara Group; North 
America. 
Ptychocrinus, W. and Sp. Like Thysanocrinus, but arms uniserial. Ordovician ; 
North America. 
Idiocrinus, W. and Sp. JR represented by a single large interbrachial in 
each of the interrays ; that of the posterior side resting upon JRA. Niagara 
Group ; North America. 
Spyridiocrinus, Oehlert. Devonian; Saint Malo, France. 
Lampterocrinus, Roem. Like Thysanocrinus, but having an anal tube; [2A 
large, and succeeded by three longitudinal rows of Jk. Silurian (Niagara 
Group) ; North America. 
Orthocrinus, Jaekel. Devonian ; Rhineland. 
Family 7. Rhodocrinidae. Roemer. 
Base dicyclic. Infrabasals five ; basals five, pentagonal, truncated at the upper end. 
The radials separated all around by large interradials. Anal area but very slightly, 
often not at all different from those of the other interrays. The rays generally free 
above the distichals ; primary arms rarely more than ten, and either simple or branching. 
Pinnules long and closely abutting. Ordovician to Sub-Carboniferous. 
Rhodocrinus, Miller (Acanthocrinus, Roem.) Calyx small, composed of delicate 
plates. JB frequently hidden by the column. & and JF large; the latter 
rapidly decreasing in size upward. Rays free from the distichals upward, and 
the ten primary arms branching once or oftener in the free state. Arms biserial, 
thin, and moderately short; pinnules closely crowded, long, and slender. Column 
round ; axial canal stelliform. Ordovician to Middle Sub-Carboniferous ; Europe 
and North America. 
Archaeocrinus, W. and Sp. Calyx obovate. J numerous, and enclosing 
a supplementary anal in the second or third row. Interdistichals generally 
present. Arms uniserial, branching. Ordovician ; Canada. 
Lthaphanocrinus, W. and Sp. Like the preceding, but with large JB, 
which are exposed in a side view. Arms long, simple, and uniserial. Ordo- 
vician ; Ohio and Indiana. 
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