152 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



but the infrabasals are fused with the top stem joint, whicli throughout this 

 order is not the youngest joint of the stem. 



To the Articulata we refer the Ichthyocrinidae, and all Mesozoic and later 

 Crinoids — recent and fossil — in which the new stem joints are introduced 

 beneath the top joint. They are divisible into two suborders : — 



I. The Articulata Impinis^ata, to include the Ichthyocrinidse which are 

 destitute of pinnules. 



II. The Articulata Pinnata, to include those families in w^hich pin- 

 nules are present. 



That there exists a close resemblance between the Ichthyocrinidse and Coma- 

 tulae — especially their earlier stages — is well shown by our illustrations 

 on Plate VI. Figs. 13 to 20, and it is worth mentioning that no other form 

 has changed so little in geological time as the genus Ichthyocrinus, which 

 survived from the Lower Silurian to the Coal Measures, and which may be 

 regarded as the ancestor of all Articulata. 



The name "Articulata" was proposed by J. S. Miller, and adopted by 

 Johannes Miiller for a subdivision of the Crinoidea. The former referred to 

 it Apiocrinus, Uncrinus, and Pentacrinus, to which Miiller added the Coma- 

 tul^. He defined the group as one in which the lower ray plates are con- 

 nected laterally by a skin, which may be naked, or paved with irregular 

 plates. From this definition we judge that his ideas of the group were 

 substantially the same as ours, and we believe if Miiller had known the 

 Ichthyocrinid^, he would have placed them together with the Apio- 

 crinidae and Comatulse. His definition, however, is not complete enough, 

 and it admits forms which in our opinion are widely different. We al- 

 lude to the Encrinid^ and Pentacrinidae, which differ from the Apio- 

 crinidaB and Comatulas in having the uppermost joint of the stem the 

 youngest joint, whereas in the latter two it is not. That MUller admits 

 Pentacrinus into this group we can understand — its lower brachials actually 

 are united by a skin — but it is difficult to see why he added the genus 

 Encrinus, in which the rays are free from the radials up. The Pentacrinidee 

 have through the Encrinida) close affinities with the Poteriocrinidse, and are 

 probably their descendants; but if they are Inadunata, they represent an 

 aberrant type, for their lower brachials, as stated before, are enclosed in the 

 calyx. This departure from the Inadunate plan may perhaps be explained 

 if we consider that the calyx of the Pentacrinidae, owing to the reduction of 



