CLASS I 



CYSTOIDEA 



157 



Order 4. APORITA Zittel (emend.). 



Radial symmetry affects food-grooves and calyx plates. Food-grooves hörne on 

 processes aroimd the oral centre. No folds, rhombs or diplopores. 



This division is admittedly artificial and ill-defined, being chiefly a 

 receptacle for genera whose relations are imperfectly understood, or whose 

 systematic position is doubtful. 



Family 1. Oryptocrinida© Zittel. 



Calyx composed of three rings of very finely perforate or imperforate, somewhat 

 regularly arranged plates. Mouth central, surrounded hy articular facets for the 

 attachment of small arms. Anus eccentric ; stem round and 

 slender. Ordovician to (?) Permian. l iH 



Cryptocrinus v. Buch (Fig. 248). Base composed of 

 three plates, and surmounted hy two zones, each con- 

 taining five plates of unequal sizes. Mouth and anus 

 enclosed within a ring of smaller pieces. Ordovician ; 

 St. Petersburg. G. cerasus v. Buch. 



Lysocystites Miller (Echinocystites Hall non Wyv. 

 Thomson, Scolocystis Gregory). Silurian (Niagara 

 Group) ; North America. 



Hypocrinus Beyrich. This a i 



genus, described as a Cystid, 

 from the Permian in the Island 

 of Timor, and Coenocystis Girty, 

 from the same formation in 

 western America, are probably 

 Crinoids. 



Family 2. 



Macrocystellidae 

 Bather. 



Fia. 248. 



Crijptocrinuscerasnsw Buch. 

 Ordovician ; Pulkowa, Russia. 

 a, b, c, Calyx from one side, 

 from above, and from below 

 (nat. size); m, Mouth ; a, Anus. 



Fig. 249. 



Macrocystella manae Call. 

 A, from side x 1/1. B-D, por- 

 tion of a brachiole, x8/l, 

 from side, dorsal and ven- 

 tral surfaces. B, Single plate 

 enlarged (after Bather). 



Calyx consisting of three or four 

 circlets of plates, displaying more 

 or less pentamerism. No pores ar 

 rhombs. Cambrian. 



Macrocystella Calloway. 

 (Mimocystites Barr.) (Fig. 249). Three ranges of five plates each, followed 

 by a fourth of the same number bearing bifurcating brachioles. Radiating 

 folds strongly marked, dividing surface into triangles. No rhomb structure 

 visible. Stem rapidly tapering. Pentamerous symmetry is well marked, 

 and the form might be characterised as a tri-cyclic Crinoid. Cambrian ; 

 England. 



Lichenoides Barr. (Lichenocystis Haeckel). Cambrian ; Bohemia and 

 Bavaria. Aethocystis S. A. Miller. Silurian ; Indiana. 



Family 3. Tiaracrinidae Bather (emend.). 



Calyx composed of not more tjian two circlets of plates : three (hasdls) in the first, 

 and four (radials) in the second ; followed hy a ränge of short plates resemhling 



