6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



and significance a true proximale, never succeeds in attaching itself 

 permanently to the calyx. 



Thus upon close analysis neither the cirri nor the paired division 

 series are found to be in reality new structures ; the cirri, which occur 

 sporadically in certain of the older types as well as uniformly in 

 many of the later, are always associated with atrophy, dwarfing or 

 attenuation of the column, and are in reality merely the evidence of 

 the diversion of the column-forming substance from its original 

 intent in the direction of the production of imperfect fractional 

 columns, while the paired division series are merely reduplications 

 of the primitive arm base, made necessary by the atrophy of the 

 calyx and the consequent creation of a gap between the radials, of 

 necessity in contact with the true calyx plates, and the arm bases, of 

 necessity situated on the border between the ventral and the lateral 

 surfaces of the animal. 



THE CONTRASTING CHARACTERS USED IN DIFFERENTIATING 

 THE GROUPS OF RECENT CRINOIDS, WITH THE FAMILIES 

 EXHIBITING EACH, AND AN EXPLANATION OF THEIR DIF- 

 FERENTIAL AND PHYLOGENETIC SIGNIFICANCE 



In the following pages, grouped under the headings " I. Calyx, 

 II. Column, III. Disk, IV. Arms, V. Pinnules and VI. General," 

 are listed all of the more important differential characters of broader 

 significance found in the recent crinoids. 



These characters are given in contrasting pairs, the more general- 

 ized being in each case numbered " I " and the more specialized 

 numbered " 2." 



In each of these pairs the more specialized character (2) is always 

 derived from the more generalized by a process of degeneration 

 through reduction or more or less complete suppression. 



Under each member of each pair are grouped the families pre- 

 senting the character as described with its bathymetric and thermal 

 distribution, and after each pair the significance of the two con- 

 trasting characters is pointed out, as well as the significance of the 

 difference between them. 



1. CALYX 

 1. Calyx in the form of a cup, protecting the viscera dorsally and 



laterally. Bathymetric Thermal 



range range 



Holopodidse 5-120 71.0 



Plicatocrinida; 266-2575 31. 1-43.9 



