8 INTRODUCTION. 
ous ways to Mr. Asa S. Tiffany, of Davenport, Dr. C. C. Washburn, of Wal- 
dron, Ind., Dr. Moses Elrod, of Hartsville, Ind., Rev. H. Herzer, of Berea, 
Ohio, Rey. John Davis, of Louisiana, Mo., Mr. D. H. Todd, of Kansas City, 
Mo., Mr. G. M. Nickels, of Sparta, Ill, Mr. E. Brown, of Belfast, N. Y., and 
others. 
To Dr. Horace G. Griffith, formerly of Burlington, now of Philadelphia, 
we express our grateful acknowledgments for his intelligent and unremitting 
efforts to aid us in the prosecution of this work, and for his steadfast devo- 
tion to our interests manifested upon every occasion. 
We also bear in kindly remembrance our former townsman, Mr, James 
Love, whose fine collection was always at our disposal, and which, together 
with one made by Mr. J. W. Giles, afterwards passed into our hands. 
Dr. Charles R. Keyes has at all times exhibited a lively interest in the 
progress of our work, and we owe to him not only the procurement of some 
valuable specimens, but other friendly offices. 
Nor do we forget our good friend, Orestes St. John, whose keen eye and 
rare judgment, and no less his skilful pencil, have always been at our ser- 
vice. We have from him some unsurpassed structural drawings, and he 
presented us several unique Crinoids from the Coal Measures of Kansas. 
Our thanks are due to Mr. Wm. F. E. Gurley, of Danville, Ill., for the 
use of specimens from Waldron, and to Mr. A. C. Benedict, of Indianapolis, 
for the use of specimens obtained by him at St. Paul, Ind. 
In addition to the facilities above mentioned, we have had during the 
preparation of this work our own collection, which contains authentic speci- 
mens of nine-tenths of the species of Crinoids described from the United 
States, and two-thirds of all the European species. From many of the typical 
localities we have been able to obtain, either by purchase of local collections, 
or by personal exertions, large series of specimens, by means of which it has 
been possible to study in many cases, and among different genera, the indi- 
vidual variation existing in the limits of a species, and the modifications due 
to growth. 
In looking over the descriptions it will probably surprise some of the 
authors to find so many of their species placed in the synonym lists, but 
we were obliged to do so after careful study and comparison with authentic 
specimens. 
CHARLES WACHSMUTH. 
FRANK SPRINGER. 
Burtinecton, Towa, May 1, 1894. 
Received at Cambridge, September 1, 1894. 
ALEXANDER: AGASSIZ. 
