12 



SMITHSONIAN MISCELLANEOUS COLLECTIONS .VOL. 65 



The reduction of the basals and their fusion into a single calcareous 

 element is evidence of the inhibition and suppression of the normal 

 skeleton forming power by which the basal ring primarily develops 

 from five distinct centers in the form of a circlet of five similar large, 

 separate and perfect plates. 



Frequency at different depths 



Frequency at different temperatures 



Pentacrinitidse (7 'elio crinns , Hypa- 

 locrinus, Metacrinus, Isocrinus) . 5-1350 



2. Infrabasals absent, or fused with other plates. 



Bathymetric 

 range 



Pentacrinitidse (Comatulida, and 



Endoxocrinus) 0-2900 



Bourgueticrinidse 62-2690 



Holopodidse 5~ I2 o 



Plicatocrinida? 266-2575 



36.0-71.0 



Thermal 

 range 



28.7-80.O 



29.1-70.75 



71.0 



3 1. 1-43.9 



The infrabasals, which correspond to the oculars of the echinoids, 

 do not appear to be of such fundamental significance as their repre- 

 sentatives in that group, for in the earlier crinoids they may or may 

 not be present. But whatever their status in the ancient types may 

 be, they are regarded as either actually or potentially present in the 

 order Articulata, to which all but one of the recent families belong. 



