PREFATORY NOTE. 249 



for the present work. Indeed the CocJiliodonts and Myliodonts alone 

 would require space equal to that here devoted to the Hybvdonts and 

 Petalodonts. It is a matter of time, and ample at that, for the entire 

 work to reach completion ; and in the respite which necessity compels, 

 it is to be hoped that no opportunity will be allowed to escape whereby 

 additional data and collections may add to and perfect our knowledge 

 of the history of these fragmentary and for the most part scattered 

 remains of the earliest vertebrates in our earth's history. 



We have also received many courtesies from other sources, which 

 have enabled us to avoid the perpetration of errors in nomenclature, 

 besides adding much information which will be of value in monograph- 

 ing the carboniferous fishes. Dr. Joseph Leidy has not only furnished 

 ns, at our solicitation, with important references to his own labors in this 

 field, but he kindly secured for us the loan of the original specimens 

 described by him, from the Museum of the Academy of ^Natural 

 Sciences of Philadelphia. Mr. F. B. Meek also forwarded us for exam- 

 ination such specimens as have found their way to the great collections 

 of the Smithsonian Institution, from the surveys of Dr. Hayden, Lieut. 

 Wheeler, and others. And Prof. Safford placed in our hands such 

 fish remains as he has come upon in his geological investigations in Ten- 

 nessee. In connection with this work we have also had occasion to 

 acquaint ourselves with facts occurring abroad and which it was not 

 possible to obtain from our own resources. We would here acknowledge 

 the highly interesting communication with which Lord Enniskillen has 

 favored us, especially with reference to the Cochliodonts, which it was 

 our intention at one time to include in the present work. We would 

 also refer to the very favorable opportunities which one of the writers 

 owes to Dr. Chas. A. White, for prosecuting examinations intimately 

 connected with the study of the Fossil Fishes as they occur throughout 

 the Carboniferous deposits in the State of Iowa, and which have enabled 

 us the more successfully to compare the stratigraphy of the two 

 regions on either side of the Mississippi. 



In the execution of the lithographing of the plates illustrative of the 

 subjoined text, Mr. Mayer has exercised a degree of patience with our 

 wishes, and skill, for which the plates themselves are sufficient witness. 



