CLASS ii CYSTOIDEA 177 



Crinoidal fragments have been detected in the Cambrian, but consist of 

 stem-joints only (Dcii'/m'-rimis). The Ordovician of England also yields a 

 \urirty of stem-joints, and well-preserved calices of Hybocrinus and Baerocrinus 

 occur in rocks of the same age in the vicinity of St. Petersburg. In North 

 America, also, the Trenton and Hudson River limestones are locally very 

 rich in Crinoid remains. The Silurian localities of Dudley and Wenlock, 

 England, and especially the island of Gottland, Sweden, are famous for the 

 surprising abundance and exquisite state of preservation of their fossil 

 Crinoids. The Swedish forms alone comprise 43 genera and 176 species. 

 The Silurian of North America, notably the Niagara Group, likewise 

 contains a large variety of forms. 



The best known Devonian localities are the Eifel, Rhineland, Nassau, West- 

 phalia, the Ardennes, Asturias, Departement Mayenne, and North America. 

 The Carboniferous Limestone of Tournay and Vise", Belgium, and that of Eng- 

 land, Ireland, and the vicinity of Moscow, Russia, is occasionally charged with 

 exceptionally well-preserved Crinoidal remains. But the most famous of all 

 horizons is the Sub-CarboniferouS Limestone of North America, where, in 

 particular, the localities of Burlington, Iowa, and Crawfordsville, Indiana, 

 have acquired a world- wide reputation. 



The Permian has yielded but a single genus, which is doubtfully referable 

 to Cyathocrinus. From the Trias only the Encrinidae and a few species of 

 Pentacrinus are as yet known. The remaining members of the Articulata 

 make their appearance in the Jura and Cretaceous, and with the exception of 

 the Saccocomidae, are still represented in the existing fauna. 



Class 2. OYSTOIDEA. Leopold von Buch. 1 



Extinct, pedunculate, or more rarely stemless Pelmatozoa, with calyx composed of 

 more or less irregularly arranged plates. Arms imperfectly developed, sometimes absent. 

 Calyx plates often finely perforate. 



The calyx is globose, bursiform, ovate, or ellipsoidal in form, more rarely 



1 Literature: 



Volborth, Alex, von, Ueber die Echinoencrinen (Bull. Acad. Imp. Sc. St. Petersb. vol. X.), 1842. 

 Volborth, Alex, von, Ueber die russischen Sphaeroniten (Verhandl. Mineralog. Gesellsch. St. 



Petersb.), 1845-46. 

 Buch, Leopold von, Ueber Cystideen (Abhandl. der Berliner Akad. fiir 1844), 1845. Translated 



in Quart. Journ. Geol. Soc. London, 1845. 

 Forbes, Edward, On the Cystidea of the Silurian Rocks of the British Islands (Mem. Geol. Survey 



Great Brit. vol. II., part 2), 1848. 



Miiller, Johannes, Ueber den Bau der Echinodermen (Abhandl. der Berliner Akad.), 1853. 

 J/n/f, Jtnnen, Palaeontology of New York, vol. II., 1852, and vol. III., 1859. 

 Billings, E., On the Cystidea of the Lower Silurian Rocks of Canada (Figures and Descriptions of 



Canadian Organic Remains, Decade III.), 1858. 

 Hall, James, Descriptions of some new Fossils from the Niagara Group (20th Ann. Rept. N.Y. 



State Cabinet of Nat. Hist.), 1867. 

 Billings, E., Notes on the Structure of Crinoidea, Cystidea, and Blastoidea (Sil. Amer. Journ. 



Sci. 2nd ser.), vol. XLVIII., 1869, and XLIX., 1870. 

 Volborth, Alex, von, Ueber Achradocystites uud Cystoblastus (Mem. Acad. Imp. Sci. St. Petersb., 



vol. XVI.), 1870. 

 Schmidt, Fr., Ueber Baltisch-Silurische Petrefacten (Mem. Acad. Imp. Sci. St. Petersb., vol. 



XXI.), 1874. 



Barrande, Joachim, Systeme Silurieu du Centre de la Boheme. Cystidees, vol. VII., 1887. 

 Carpenter, P. H., On Certain Points in the Morphology of the Cystidea (Journ. Linn. Soc. vol. 



XXIV.), 1891. 



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