THE CRINOIDEA FLEXIBILIA 



By FRANK SPRINGER 



ASSOCIATE IN PALEONTOLOGY, U. S. NATIONAL MUSEUM 



INTRODUCTION 



It is a fresh illustration of the growth of knowledge that the division of the 

 Crinoidea which forms the subject of the present memoir was not known at all 

 to the earlier systematic writers who treated of the Class ; neither to J. S. Miller, 

 with whose epoch-making monograph the systematic study of the crinoids as a 

 group began nearly a century ago, nor to Johannes Muller, whose masterly 

 researches upon the anatomy of the Echinoderms 20 years later laid the founda- 

 tion for future investigations upon their structure. The magnitude of the 

 group as now understood is shown by the size of this treatise ; and the progress 

 above alluded to is further exemplified by the manner in which the subject has 

 expanded under my hands. 



When I began the study of the Flexibilia after the death of Wachsmuth in 

 1896, it was part of a more ambitious plan to work up the two groups remaining 

 after the Camerata; and of these it was supposed that the present group would 

 be relatively a minor undertaking. I estimated that 25 plates would contain all 

 the necessary illustrations, and that these with the text would fall readily within 

 the compass of a single volume. All the known material of this group in the 

 museums of the world at that time did not occupy one-fourth of the space that 

 is now required for the specimens of my own collection. Except for a few 

 species, the Flexibilia are the rarest of all the fossil crinoids, some forms being 

 represented by a single specimen, and most of them by only a few. It was my 

 early perception of the inadequacy of material, of the necessity of making 

 further collections, and of examining as far as possible the types and other speci- 

 mens from all sources, that has in part caused the long delay in the' preparation 

 and publication of this work. Far the greater part of the delay, however, has 

 been due to the desultory character of my studies, arising from causes not within 

 my control. The insistent demands of an exacting profession, and the claims 

 of business affairs which absorbed the major portion of my time, caused fre- 

 quent and often long breaks in the prosecution of the work, the total of which 

 must be measured by years. 



These interruptions, however, have not been without their compensating 

 advantages ; for during all this time the acquisition of new material, chiefly 

 through the medium of collectors in the field, has been steadily going on, result- 



