INTRODUCTION. 



The present work is the outgrowth of studies begun over twenty years 

 ago under the encouragement of Prof. Louis Agassiz, and prosecuted con- 

 tinuously ever since. During that time, we made two very large crinoidal 

 collections, of which the original one, in 1873, was secured by Prof Agassiz, 

 for the Museum of Comparative Zoology. Upon this collection one of the 

 writers, while an assistant at the Museum, laid the foundation of the present 

 w^ork. Since 1877 the investigations were conducted by us jointly, and 

 during that time we have built up together the extensive collection which 

 is known as the collection of Wachsmuth and Springer. The advantage of 

 residing, for a time both of us, at Burlington, a locality so well known for 

 the wealth of its crinoidal remains, gave us excellent opportunities to study 

 the Crinoids in all stages of preservation, and being in the field ourselves, we 

 could pick up such material as would help us in the study of minute details. 



Since the publication of our first paper on the Crinoids, it has been our 

 aim to direct our special attention to studying the morphology of the vari- 

 ous groups as they appeared to us, with a view to future classification, and 

 to revise the work of the previous writers. The various classifications which 

 had been proposed were not based upon strictly morphological principles, and 

 in many cases widely distinct forms were placed together in the same group. 



It early became evident to us that we could not hope to gain a correct 

 understanding of the fossil forms except by studying their living represen- 

 tatives. The publication of Carpenter's two Challenger Reports, and De 

 Loriol's important Monograph on the Mesozoic and later Crinoids of France, 

 opened to the working palaeontologist a new field of. research, and enabled 

 him to study the relations between palaeozoic and neozoic Crinoids, which 

 had been altogether misunderstood. It had been the general opinion, ever 

 since the time of Johannes Miiller, that all palaeozoic forms were widely 

 distinct from the later ones, a view also held by us until 1890. 



Before the publication of the first Challenger Report, the attention of 

 paleontologists had been directed almost exclusively to the structure of the 

 dorsal or abactinal side of the calyx; that of the ventral side had been very 

 much neglected, and scarcely any attempt had been made to homologize the 



1 



