142 



THE CRINO1DEA 



The Classification here adopted keeps accepted terms so far as 

 possible, but the distribution of the groups is very different from that 

 hitherto accepted. Dividing all Crinoidea into MOXOCYCLICA and 

 DICYCLICA, we trace in each order a gradual and to some extent parallel 

 modification, here and there diverging in somewhat similar directions. 

 Thus the simplest forms in each order are INADUNATA, with free distinct 

 arms, and pass from a Larviform stage, with simple tegmen, to a Fistulate 

 stage, with more complex anal tube and tegmen. At an early period 

 (? Cambrian) in the history of the Monocyclica, the Camerate modification, 

 viz. rigid incorporation of brachials in cup and ambulacrals in tegmen, 

 affected a few forms, and thus arose MONOCYCLICA CAMERATA. At a later 

 period (Silurian) was a repetition of this modification, but one affecting the 



MONOCYCLICA. 



DICYCLICA. 



INADUNATA. 



k 



Cambrian. (LARVIFORMIA). 



Ordovician. 



Silurian. 



ADUNATA. 



FIG. LVI. 



Supposed Relations of the Orders and 

 Sub-Orders of Crinoidea. 



I 



Devonian. 

 Carboniferous. 



Permian. 



Trias. 



Jurassic. 



Cretaceous. 



Tertiary. 



Recent 



cup to a far less extent, and resulting chiefly in a solid tegmen and biserial 

 arms ; thus arose the MOXOCYCLICA ADUNATA (or Platycrinoidea), which 

 even Wachsmuth and Springer find a difficulty in placing with the 

 Camerata. These two highly specialised branches died out before the 

 close of the Palaeozoic epoch, the Adunata outliving the Camerata ; but 

 the simpler Inadunate forms continued, and reached a high degree of 

 specialisation in their Jurassic descendants, to which the living Hyocrinus 

 is closely related. The Dicyclica Inadunata similarly gave off the 

 DICYCLICA CAMERATA, which persisted only a little less long than their 

 monocyclic convergents. The dicyclic Crotulocrinidae of the Silurian 

 are curiously parallel to the Monocyclica Adunata, but it is not worth 

 while to separate them from the typical Inadunata. About the same time 

 arose among the Dicyclic Inadunata the modification that resulted in 

 the FLEXIBILIA, with brachials loosely incorporated in dorsal cup. The 



