4 INTEODUCTION. 



Not the least of the pleasure we find in bringing our work to a conclusion 

 is the opportunity it affords us of acknowledging our obligations to the men 

 of science and collectors of America, for their liberality and personal con- 

 fidence shown to us, by placing in our hands — often for indefinite periods 

 — original, unique, and priceless collections, without the use of which this 

 work would have been impossible. It would be difficult to express in fitting 

 terms of acknowledgment the full measure of our indebtedness to them, and 

 we can only venture the hope that they may find in the work itself some 

 small return for the valuable contributions they have made toward it. 



To Mr. Agassiz we owe a lasting debt of gratitude : first of all for his 

 personal encouragement and valuable counsel, and next for the use of the 

 magnificent collection of the Museum of Comparative Zoology. This has 

 been placed at our disposal without restriction, not only for examination at 

 Cambridge, but for removal to Burlington of all specimens we desired, with 

 liberty to use them as if they were our own. Only those who are acquainted 

 with the character and value of this unrivalled collection can appreciate our 

 obligation for such a use of it. It contains the original collection of De 

 Koninck, of the Belgian Carboniferous Crinoids, and the Schultze collection 

 from the Devonian of the Eifel, — by far the finest collections that have 

 ever been made of the rare Crinoids of those interesting localities. There 

 are also the collections made by Hon. B. J. Hall, Prof. W. H. Barris, and 

 the original collection of Wachsmuth, all from the Burlington limestone, 

 which include the types of a large number of the species described by Hall, 

 White, and Meek and Worthen. In addition to these is the fine collection 

 made by C. B. Dyer, from the Hudson Eiver group, of Cincinnati, con- 

 taining many types of species described by Meek in the Ohio report, besides 

 most excellent material from Waldron, Crawfordsville, and other celebrated 

 localities of the West ; also the Walcott collection from New York. 



A full account of the various collections made use of by us would 

 exceed the limits of a preface, but we cannot refrain from making par- 

 ticular mention of some of them : — 



The collections in the American Museum of Natural History at New 

 York, containing many of the type specimens of the New York Palasonto- 

 logical Keports, have been at all times accessible to us through the courtesy 

 of Prof R. P. Whitfield, who has been prompt to send us such specimens as 

 we needed for illustration or comparison, and to give us any desired infor- 

 mation obtainable from the extensive material under his charge. 



