NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 65 



It differs from the sequence of the families on the basis of the 

 uncorrected figures for the structural units in that the position of 

 the Bourgueticrinidse and the Apiocrinidse is reversed. 



If we judge the phylogenetic status of the Pentacrinitidse on the 

 basis of its average development, by considering only the character 

 in each pair having the majority representation and leaving out of 

 consideration the primitive features exhibited only by a negligible 

 percentage of the species, the Pentacrinitidse occupy a position well in 

 advance of that of the Holopodidse. 



The Bourgueticrinidse and the Apiocrinidse undoubtedly are on 

 very nearly the same plane, as is evident on even a superficial survey 

 of their fossil species. Judging from the general structure of the 

 recent genera the disk of the recent Apiocrinidse, as yet not known, 

 is probably more like that of the stalked pentacrinites than like that 

 of the Bourgueticrinidse or of the comatulids ; if so, this would 

 emphasize the phylogenetically advanced position of the Bourgueti- 

 crinidse. 



From the three tables showing the relative phylogenetic status of 

 the crinoid families including recent species we get the following 

 differences between each family and the family below it : 



1) V « 1) N 



Q\0 gvo gvo 



2<i °d 2d 



fe fe Ph 



Pentacrinitidse 6 _ 33 40 



Holopodidse 4 31 6 



Bourgueticrinidse o 61 46 



Apiocrinidse 5 13 12 



Phrynocrinidse 14 74 55 



Plicatocrinidse o 



This indicates that there is a very broad phylogenetic gap between 

 the Plicatocrinidse (belonging to the Inadunata) and the remaining 

 families (all of which belong to the Articulata). There is another 

 broad gap between the Bourgueticrinidse and the Apiocrinidse. 



Thus it would appear that the crinoid families represented in the 

 recent seas, on the basis of their recent representation, fall into three 

 well marked groups separated by broad phylogenetic gaps, as follows : 



Group 1 Group 2 Group 3 



Pentacrinitidse ...... 



Holopodidse „, ... Plicatocrinidse 



t, . . . , Phrynocrmidse 



Boursfueticnmdse 



