154 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



the base flat or truncated ; plates twenty-five in number. Arms sometimes 

 bifurcating. Silurian ; North America. 



Apiocystites Forbes. Calyx regularly oval, elongate or slightly compressed, 

 and composed of nineteen plates. Silurian ; England, Sweden and North 

 America. 



Hallicystis Jaekel. Like the preceding, except in having five deltoid 

 plates instead of one. Silurian. 



Lepocrinites Conrad (Lepocrinus or Lepadocrinus Hall ; Staurocystis Haeckel). 

 Silurian ; New York and Tennessee. 



Lepadocystis Carp. {Meehocystis Jaekel). Ordovician ; North America. 



Sphaerocystites Hall ; Coelocystis, Jaekelocystis, Tetracystis and Trimerocystis 

 Schuchert. Silurian ; North America. 



Strohilocystites White. Devonian ; North America. Hybocystites Wetherby 

 Silurian ; North America. 



Fig. 242. 



Calloeystites jewetti Hall. Sil- 

 urian (Niagara Group) ; Lock- 

 port, New York. Calyx seen 

 from one side (natural size). a, 

 anus ; hr, bracliioles, j-), pectino- 

 rhombs. x § (after J aekel). 



Fio. 243. 



Pleurocystites filüextus Billings. Ordovician ; Ottawa, 

 Canada. A, Calyx from the anterior side. B, Same 

 from tlie anal side ; A, anal area ; a, anus ; h, basals ; 

 br, bracliioles ; g, genital aperture ; l 1-2, laterals ; m, 

 madreporite. x | (after Jaekel). 



Subfamily B. Glyptocystinae Jaekel. 



Pleurocystites Billings (Fig. 243). Convex side with large plates arranged 

 in cycles ; flattened side covered with very minute plates. Three isolated 

 pore-rhombs borne on the convex side. Arms two in number, robust. Stem 

 round, tapering distally to a point. Ordovician ; Canada. 



Glyptocystites Billings. Ordovician ; Canada and Russia. 



Cheirocrinus Eichwald ; Cystoblastus Yolborth. Ordovician ; Russia. 



Homocystites Barrande. Ordovician and Silurian ; Bohemia. 



Subfamily C. Echinoencrininae Jaekel. 



Echinoencrinus v. Meyer {Sycocystites v. Buch and Gonocrinites Eichw.) (Fig. 

 244, A). Calyx composed of four basal plates, and three cycles containing five 

 plates each. All calycine plates ornamented with costae or ridges radiating 



