INTRODUCTION. 
Tue 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 crincidal 
collections, of which the original one, in 1873, was secured by Prof. Agassiz, 
for the Museum of Comparative Zodlogy. Upon this collection one of the 
writers, while an assistant at the Museum, laid the foundation of the present 
work. 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 paleontologist a new field of research, and enabled 
him to study the relations between paleozoic and neozoic Crinoids, which 
had been altogether misunderstood. It had been the general opinion, ever 
since the time of Johannes Miiller, that all paleeozoic 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 
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