CRINOIDEA. 



295 



anal interradius and of ten a radianal. 5 oral plates and high ventral tube. 

 Arms long, much branched, uniserial, without pinnules. U. Cambrian to 

 Carboniferous. Cyathocrinus Miller (Fig. 200), Barycrinus W. and S., 

 Homocrinus Hall, Lecythocrinus Mull., Arachnocrimis M. W., Gissocrinus 

 Ang., Porocrinus and Carabocrinus Billings. 



Fam. 9. Crotalocrinidae. Dicyclic ; calyx of 5 infrabasals, 5 basals, 

 5 radials, and a small anal interradial. Lower brachials laterally in con- 

 tact. Arms much branched, and branches 

 connected. No pinnules. Axial canals in 

 arm-plates. Silurian. Crotalocrinus Austin, 

 Enallocrinus d'Orb. 



Fam. 10. Poteriocrinidae. Dicyclic. 5 

 infrabasals sometimes hidden by the column, 

 5 basals, 5 radials ; 1-2 interradial anals 

 and often a radianal. Ventral sac large. 

 Arms simple or branched, with long pin- 

 nules ; uniserial, alternate, rarely biserial, 

 Devonian and Carboniferous. Poteriocrinus 

 Miller (Figs. 192,201), Woodocrinus de Kon., 

 Scaphiocrinus Hall, Agassizocrinus Troost, 

 Cromyocrinus and Phialocrinus Trautsch., 

 Erisocrinus M.W., Stemmatocrinus Trautsch. 

 In the last two genera the interradial plate 

 of the anal interradius is very small or 

 absent. 



o 



FIG. 201. Analysis of the cup of 

 Poteriocrinus (from Zittel, 

 after Bather), a special anal, 

 a' interradial anal, ra radianal, 

 r radial, b basal, ib infrabasal, 

 br' primibrach. 



Order 3. CAMERATA. 



The calyx is enlarged by the incorpora- 

 tion of the proximal brachials : * it con- 

 sists of a monocyclic or dicyclic base, a 

 circle of radials, and of a certain number 

 of the proximal brachials. The latter are connected by interradial 

 (interbrachial) plates ; the plates of the anal interradius being more 

 numerous than the others. The radials are in contact all round (Melo- 

 crinidae, Calyptocrinidae, Platycrinidae) ; they are separated only in 

 the anal interradius by an anal plate (Thysanocrinidae, Batocrinidae, 

 Actinocrinidae, Crotalocrinidae, Hexacrinidae) ; they are separated 

 all round (Rhodocrinidae). Infrabasals are present or absent. The 

 calyx-cover is a vault of solid plates firmly connected together. The 

 mouth is central and covered with 5 firmly united oral plates the hinder- 

 most of which is often the largest and projects in between the four others. 

 The orals are sometimes quite inconspicuous. The interambulacral plates 

 of the calyx-cover sometimes project over and cover the ambulacral 

 plates (Fig. 193). The mouth being covered up by the orals, its only 

 communication with the exterior is through the ambulacral canals, which 

 open at the base of the arms and branch as often as the arms branch before 

 leaving the calyx. Anus excentric or subcentral, often at the end of a 

 proboscis-like prolongation. The plates of the calyx are connected by 

 simple, smooth sutural surfaces. They are sometimes continued without 

 any break into the interambulacrals of the calyx-cover. Arms with one 

 or two rows of brachials, usually with pinnules. Dorsal canals have 

 not been observed in the brachials. U. Cambrian to Carboniferous. 



Except in some Platycrinidae. 



