188 ECHINODERMATA PELMATOZOA SUB-KINGDOM in 



are separated by small furrows conducting into the ambulacral grooves. Anus 

 closed by a valvular pyramid. Ordovician ; Russia, Bohemia. 



Asteroblastus, Eichw. (Fig. 311). Calyx gemmiform, pentagonal, pedun- 

 culate, and composed of innumerable rigidly united plates which are per- 

 forated by conjugate pores. Upper surface marked by five large petaloid 

 or stellate areas, which are covered with alternating plates, and correspond 

 to the recumbent arms of Agelacrinus. Ordovician ; Russia. 



Tiaracrinus, Schliit. (Staurosoma, Barr.) Devonian ; Eifel, Bohemia. 



Range and Distribution of the Cystoidea. 



Not only are the Cystideans wholly extinct, but they also constitute the 

 oldest known group of the Pelmatozoa. They are represented in the Cam- 

 brian by a number of poorly preserved forms, whose affinities are in many 

 cases doubtful (Protocystites, Macrocystella, Eocystites, Lichenoides, Trochocystites) i 

 They attain the climatf of their development in the Ordovician and Silurian, 

 whereupon they suddenly diminish in numbers, and with the close of the 

 Carboniferous they entirely disappear. Of the 250 species that have been 

 described, scarcely a dozen are found in strata above the Silurian. 



Although a few forms (Echinosphaerit&s, Aristocystites, Caryocystites) appear 

 in considerable abundance in certain formations, and occasionally fill up 

 whole beds, the majority are of comparatively rare occurrence. The arms 

 and pinnules are only exceptionally preserved, owing to their fragile con- 

 stitution ;' and the stem is also usually lost. 



Cystideans are found most plentifully in the Ordovician rocks of St. 

 Petersburg, Russia, and in the Silurian localities of Oeland, Gottland, Sweden, 

 Wales, and Bohemia (Etage D). The Bohemian specimens are usually pre- 

 served in the form of casts and moulds, and are contained in silicious or 

 argillaceous slates. The Chazy and Trenton limestones of Canada, New York, 

 Ohio, and Indiana also yield a large variety of forms. 



Excellently preserved specimens of Pseudocrinites, Apiocystites, Echinoen- 

 crinus, and Anomalocystites are obtained from the Silurian limestones of Dudley 

 and Tividale, England ; similar, and in part vicarious forms (Lepadocrinus, 

 Callocystites, Caryocrinus) being found in the Silurian (Niagara Group) of North 

 America. Only scanty remains are known from the Devonian (Proteocystites, 

 Anomalocystites, Agelacrinus, and Tiaracrinus) ; and but two genera (Agela- 

 crinus and Lepadocrinus) are represented in the Lower Carboniferous. The 

 last surviving genus is Hypocrinus, which is confined to the Permo-Carbon- 

 iferous of Timor. 



Class 3. BLASTOIDEA. Say. 1 



Extinct, short-stemmed, or stemless Pelmatozoa with a large rigid calyx, which 

 resembles a flower-bud in shape, and is generally composed of thirteen principal 



1 Say, Thomas, Observations on some Species of Zoophytes, etc. (Am. Journ. Sci. vol. II.), 1820. 

 Say, Thomas, On two Genera and several Species of Crinoids (Joiirn. Acad. Nat. Sci. Phil ad. vol. 



IV. p. 289), 1825. (Also in Zool. Journ. vol. II. p. 311), 1825. 

 Roemer, Ferdinand, Monographic der fossilen Crinoideenfamilie der Blastoideen (Troschel's Archiv. 



fiir Naturgeschichte, Bd. XVII. pp. 326-397), 1852. 

 Rofe, John, Notes on Echinodermata (Geol. Mag., Dec. 1, vol. II.), 1865. 



