6o 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



According to the table just given the true phylogenetic arrange- 

 ment of the families of recent crinoids, together with their relative 

 positions in the scale of phylogenetic advancement, reckoning from 

 the Plicatocrinidae as the least specialized type, is as follows : 



Pentacrinitidse -\- 6 (-j- 16) or 30 (40) 



Holopodidae -j- 3 or 24 



Bourgueticrinidas — 1 or 20 + 



Apiocrinidse — 1 or 20 — 



Phrynocrinidse — 6 or 15 



Plicatocrinidae — 21 or 1 



THE RELATIVE SPECIALIZATION OF EACH STRUCTURAL UNIT 

 IN THE CRINOID FAMILIES INCLUDING RECENT SPECIES 



In the various families the several structural units are not neces- 

 sarily correlated in the amount of specialization they exhibit. The 

 sequence, in each family, as deduced from the preceding tables, is as 

 follows, the most specialized structural unit being in each case placed 

 at the head of the list, and units of equal value being bracketed. 



THE PHYLOGENETIC SEQUENCE OF THE RECENT CRINOIDS 



ON THE BASIS OF THE RELATIVE SPECIALIZATION OF 



EACH OF ITS COMPONENT STRUCTURAL UNITS 



If we take each structural unit and in each family assign to it a 

 number (from I to 6) according to its condition of specialization in 

 reference to all the other families "(if of the same value in two or 

 more families giving it the same number in each) , the family show- 

 ing the lowest total will be the one which, as the sum total of all these 

 structural units, is the most specialized. . 



The figures are given in the following table ; the figure I indicates 

 the maximum specialization for each structural unit, and the figure 6 

 the minimum. 



