2 INTRODUCTION. 



plates of the tegmen in the different groups. The first attempt in this 

 direction was made by Wachsmuth in 1877, and the subject was taken up 

 again in our Revision of 1879. Dr. P. Herbert Carpenter discussed the 

 question more elaborately in 1884, when it became manifest that our views 

 differed radically upon several important points, and especially as to the 

 identification of the oral plates. The progress of our studies on this and 

 other questions was published from time to time in the Eevision, and in 

 short papers. This was done for the double purpose of making known the 

 results of our own studies, and of stimulating inquiry by others upon points 

 that were still obscure. 



Whatever may be the merits or demerits of the Revision — and that the 

 latter are many and serious none are better aware than we — it accom- 

 plished one of its purposes. It induced research and provoked discussion 

 upon new lines and with an activity unprecedented in this field. The 

 contributions to the knowledge of the subject, resulting directly from these 

 controversies, have been of incalculable value to us, and none the less so 

 because some of our own theories have been from time to time exploded. 

 As the most important result, it has now become clear that the Crinoids 

 were most intimately connected from the Silurian down to the present 

 time, and that only the Camerata — a highly specialized type — became 

 extinct at the close of the Carboniferous. It was not until this fact was 

 realized that the way was opened to a better understanding of the whole 

 Crinoid group, in which, as so often found in Nature, the simpler forms 

 persisted, and led down to present types. Although it seems plain enough 

 now, it was only by slow steps, and after long and patient research, that 

 this result was reached. 



After a large amount of preliminary work had been done, we proceeded 

 to prepare for publication in permanent form such part of it as we could 

 reasonably hope to finish, and to that end we began the preparation of the 

 illustrations in 1887. The work has grown upon our hands to such an 

 extent that we found it necessary to limit it to the Camerata, the largest 

 and most remarkable group among Palaeozoic Crinoids. Thus limited, we 

 could hope to give a reasonably full account of this group, and in connec- 

 tion with discussion of the morphological and systematic relations of the 

 other groups, to give some account of the Crinoids generally. 



The most of the drawings were made under our personal supervision in 

 our Museum at Burlington ; a few were made in Washington. Thirty-five 



y" 



