CLASS III 



CRINOIDEA 



187 



Family 3, Dimerocrinidae Bather. (Glyptocrinidae Zittel pars ; Glyptasteridae 

 Aiigelin ; Thysanocrinidae W. and Sp.) 



Dimjclic. Lower hrachials and interhrachials forming an important pari of the 

 dorsal cup ; interbrachial s well defined. Radiais in contad except at the posterior 

 side, where theij are separated hy an anal plate. Ordovician to Devonian. 





Ptychocrinus W. and Sp. IBB five. Arms uniserial, simple, or branching 

 once. Radial and brachial plates marked by well -defined median ridge. 

 First anal plate usually succeeded by three plates in second ränge ; iBr few. 

 Anus without a tube. Ordovician ; America. 



Orthocrinus Jaekel. Arms stout and uniserial. Devonian ; Germany. 



Bimerocrinus Phillips. (Thysanocrinus 3^nd Glyptaster Hall; Eucriiius Ang.) 

 (Fig. 284). IBB five. Arms biserial, simple or branching. First anal plate 

 followed by three in second 

 ränge ; iBr in several ranges. 

 Anus without a tube. Silurian 

 to Devonian ; North America, 

 England, Gotland. 



Cyphocrinus S. A. Miller 

 (Hyptiocrinus W. and Sp.). Calyx 

 constructed as in Dimerocrinus, 

 but low and wide, with arms 

 pendent and tegmen plates spini- 

 ferous. Silurian; North America. 



Gazacrinus S. A. Miller (Idio- 

 crinus W. and Sp.). iBr limited 

 to a Single large plate in each 

 interradius, that of posterior side 

 following an anal. Silurian ; 

 North America. 



Lampterocrinus Roemer. Calyx 

 like that of Dimerocrinus, but Dinurocnnus. 

 asymmetrical from bulging at 



anal side, and with anus at end of a tube. Anal plate followed by three 

 IBB, large. Rays produced into five tubulär extensions, bearing biserial, 

 pinnuliferous arms on each side. Silurian ; North America. 



Siphonocrinus S. A. Miller. Similar to preceding, but IBB small, calyx 

 larger and more asymmetric, from subtegminal recurving of the rectum. 

 Silurian ; North America. 



Fig. 284. 

 Analysis of calyx (after W. and Sp.). 



Family 4. Rhodocrinidae Roemer. 



Dicyclic. Lower hrachials and interhrachials forming an important part of the 

 dorsal cup. Radiais separated all around hy an interradial plate followed hy well- 

 defined, definitely arranged interhrachials. Infrahasals five. Anal area slightly, 

 and often not at all, different from those of other interrays. Ordovician to Lower 

 Carboniferous. 



Rhaphanocrinus W. and Sp. (Coelocrinus Salter). Calyx obovate. Arms 



