152 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
but the infrabasals are fused with the top stem joint, which throughout this 
order is not the youngest joint of the stem. 
To the Articulata we refer the Ichthyocrinide, 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 ArticutatTa Impinnata, to include the Ichthyocrinidx which are 
destitute of pinnules. 
If. The ArticuLaTa Prynarta, to include those families in which pin- 
nules are present. 
That there exists a close resemblance between the Ichthyocrinide and Coma- 
tule — especially their earlier stages —is well shown by our illustrations 
on Plate VI. Figs. 15 to 20, and it is worth mentioning that no other form 
has changed so little in geological time as the genus Jchthyocrinus, 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. 8. Miller, and adopted by 
Johannes Miiller for a subdivision of the Crinoidea. The former referred to 
it Apiocrinus, Encrinus, and Pentacrinus, to which Miiller added the Coma- 
tule. 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 
Ichthyocrinidx, he would have placed them together with the Apio- 
crinide and Comatule. His definition, however, is not complete enough, 
and it admits forms which in our opinion are widely different. We al- 
lude to the Encrinide and Pentacrinide, which differ from the Apio- 
crinidx and Comatule in having the uppermost joint of the stem the 
youngest joint, whereas in the latter two it is not. That Miiller 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 
Enerinus, in which the rays are free from the radials up. The Pentacrinidx 
have through the Encrinid close affinities with the Poteriocrinids, 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 Pentacrinidw, owing to the reduction of 
