A PHYLOGENETIC STUDY OF THE RECENT CRINOIDS, 

 WITH SPECIAL REFERENCE TO THE QUESTION 

 OF SPECIALIZATION THROUGH THE PARTIAL OR 

 COMPLETE SUPPRESSION OF STRUCTURAL CHAR- 

 ACTERS • 



By AUSTIN H. CLARK 



CONTENTS 



PAGE 



Preface i 



The determination of the phylogenetic significance of the differential 



characters employed in systematic work 2 



The course taken by phylogenetic progression, or progressive specializa- 

 tion, among the Crinoids 3 



The apparently new structures in the later Crinoids 4 



The contrasting characters used in differentiating the groups of recent 

 Crinoids, with the families exhibiting each, and an explanation of 

 their differential and phylogenetic significance 6 



The families of recent Crinoids, with the characters, as previously given, 



presented -by each 46 



The occurrence in the various families of both components of contrasting 

 pairs 55 



The Crinoid families considered as the sum of the contrasted characters 



exhibited by them 57 



The true phylogenetic sequence of the Crinoid families having recent 



representatives 59 



The relative specialization of each structural unit in the Crinoid families 



including recent species 60 



The phylogenetic sequence of the recent Crinoids on the basis of the 



relative specialization of each of the component structural units 60 



Examination of each of the structural units in detail "i 



The corrected relative sequence of the recent Crinoids on the basis of the 

 relative specialization of each of the component structural units 64 



The relation between phylogenetic development and bathymetrical and 



thermal distribution 66 



PREFACE 



In the study of any group of animals from the systematic stand- 

 point the ultimate aim is the arrangement of the units within the 

 group in a sequence which shall conform as nearly as possible to their 

 relative phylogenetic status. 



Smithsonian Miscellaneous Collections, Vol. 65, No. 10 



