CLASS I CYSTOIDEA 145 



rule, jointed flexible arms spring from the distal ends of the ambulacral 

 grooves around the margin of the calyx ; but sometimes, as in Blastoids, arms 

 are wanting, the ambulacral areas being extended down the sides of the calyx, 

 and beset on both sides with pinnules. The inferior (dorsal, aboi-al) portion 

 of the calyx is composed of a single or double series of basal plates, which 

 rest either directly upon the stalk, or upon a centrodorsal representing a 

 single greatly enlarged columnal, or they may be grouped about a central 

 apical plate or centrale. Sometimes these plates are so small as to be invisible 

 externally, so that the calyx appears to be composed of radials only. 



The Pelmatozoa comprise three classes : Cystoidea, Blastoidea and Crinoidea. 

 Of these, the first two are wholly extinct, being confined to the Paleozoic 

 rocks ; all three are found well developed in the Ordovician, and doubtless 

 originated in pre-Cambrian time from unknown ancestral forms. The Cystids 

 are the oldest, substantially ending with the Silurian, though feebly repre- 

 sented in the Devonian and Carboniferous. The Blastoids culminated in the 

 Lower Carboniferous and ended in the Permian. The Crinoids also cul- 

 minated in the Carboniferous, but continued to survive, nevertheless, and are 

 represented in existing seas by numerous genera and species, the dominant 

 type being the unstalked forms, or Comatulids. 



Class 1. CYSTOIDEA Leopold von Buch.i 



Extinct, pedunculate, or more rarely siemless Pelmatozoa, with calyx composed 

 of more or less irregularly arranged plates. Food brought to the mouth by a system 

 of ciliated grooves, either between the calyx plates, over them, or along jnvrcsses from 

 the calyx {arms, brachioles, etc.), or subtegminal. Anus usually on the oral half of 

 the calyx. Calyx plates often perforate. Brachial processes usually imperfectly 

 developed, sometimes absent. 



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

 cylindrical or discoidal, and is composed of quadrangular, pentagonal, hexa- 

 gonal or polygonal plates, which are united by close suture. The plates 

 vary in number from thirteen to several hundreds, and only exceptionally 



1 Literature: Volhoiih, A. von, Ueber die Ecliinoeucriueti. Bull. Acad. Imp. Sci. St-Pt'tersb., 

 1842, vol. X. — Volborth, A. von, Ueber die russischen Sphaeroniten. Verhandl. Mineral. Gesell. 

 St. Petersb., 1845-46. — Buck, L. von, Ueber Cystideen. Abhandl. Akad. Wiss. Berlin, 1844 

 (1845). Translated in Quart. Journ. Geol. Soc. London, 1845, vol. ii. — Forbes, E., On the 

 Cystidea of the Silurian Rocks of the British Islands. Mem. Geol. Survey Great Brit., 1848, 

 vol. ii. part '2. — Midler, /.,' Ueber den Bau der Echinodermen. Abhandl. Akad. Wiss. Berlin, 

 1853.— ^aZZ, /., 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, J., 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. Amer. Journ. Sci. (2nd ser.), 1869, vol. xlviii., and 1870, 

 vol. xlix. — Volborth, A. von, Ueber Achradocystites und Cystoblastus. Mem. Acad. Imp. Sci. St- 

 Petersb., 1870, vol. xvi. — Schmidt, F., Ueber Baltisch-Silurische Petrefacten. Mem. Acad. Imp. 

 Sci. St-Petersb., 1874, vol. xxi. — Barrande, ./., Systeme Silurieu du Centre de la Boheme, vol. vii. 

 Cystidees, li^T .—Carpenter, P. H., On the Morphology of the Cystidea. Journ. Linn. Soc, 1891, 

 vol. xxiv. — [lae.ckel, E., Die Amphorideen und Cystoideen, etc. Festschr. fiir Gegenbaur, No. 1, 

 1896. — Jacket, 0., Stammesgeschichte der Pelmatozoen, Thecoidea und Cystoidea, 1899. — Jaekel, 

 0., tjber Carpoideen. Zeitschr. Deutsch. Geol. Gesell., 1900, vol. Hi. — Bather, F. A., Treatise 

 on Zoology (Lankester), part 3, Echinoderma, 1900. — Schuchert, C, Siluric and Devonic Cystidea. 

 Smithson. Misc. Coll., 1904, vol. xlvii. part 2.— Bather, F. A., Ordovician Cystidea from Burma. 

 Mem. Geol. Surv. India, 1906, n. s. vol. ii. — Kirk, E., Structure and relationships of certain 

 Eleutherozoic Pelmatozoa. Proc. U.S. Nat. Mus., 1911, vol. xli. No. 1846. 



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