142 



ECIIINODERMA. CRINOIDEA 



Amphoracrinus. Related to Actinocrinus. Calyx depressed, 

 saucer-like or nearly flat. Tegmen 

 much elevated. Three basals, and 

 a posterior inter-radial. Inter- 

 brachials few. Anal tube short, 

 excentric. Carboniferous. Ex. A. 

 amphora. 



B. Dicyclic Crinoids 



Cyathocrinus (fig. 57). 

 Calyx cup-like. Infra-basals small, 

 equal, pentagonal. Basals large, 

 hexagonal (except the posterior, 

 which is heptagonal and supports 

 the square inter-radial plate). 

 Radials shield-shaped. Arms uni- 

 serial, very long, bifurcating from 

 five to seven times, without 

 pinnules. Tegmen produced into 



a long anal tube. Stem round, without cirri. Silurian to Carboni 

 ferous. Ex. C. longimanus, C. acinotubus, Silurian. 



Fig. 57. Cyathocrinus longimanus, 

 from the Silurian, a, portion of 

 stem ; b, infra-basal plates ; c, 

 basals ; d, radials ; e, anal inter- 

 radial ; /, first brachial. Re- 

 duced. 



Crotalocrinus. Dorsal cup similar to that of Cyathocrinus. 

 Some fixed brachials present. Arms uniserial, dichotomous, the 

 branches uniting so as to form lamellar expansions or networks ; 

 pinnules absent. Tegmen nearly flat, formed of small plates with 

 five large plates at the centre. Anus near the posterior margin. 

 Stem thick, circular ; canal pentagonal ; roots thick. Wenlock 

 Limestone. Ex. C. rugosus. 



Botryocrinus (fig. 55). Calyx small, cup-shaped. Infra- 

 basals pentagonal ; basals hexagonal (except the two posterior, which 

 are pentagonal) ; radials with the articular surface occupying ^ to | 

 of the width ; two anal inter-radials, one as in Cyathocrinus, another 

 below it on the right. Arms divide, giving ten main branches which 

 often bear smaller branches or pinnules. Anal tube large, sometimes 



