PREFATORY NOTE. 



It was our intention, originally, to preface the work on Fossil Fishes 

 with an introductory chapter on the stratigraphic or time history of these 

 interesting remains. But as our inquiries progressed it became apparent, 

 not only that the means at the disposal of the Survey were wholly 

 inadequate to allow the completion of the investigation of the materials 

 already in hand, but that our information bearing on their distribution 

 in certain horizons was insufficient for conclusive results. We have, 

 therefore, limited our observations to such facts as are actually acces- 

 sible, believing that, so far as they go, they contribute something to 

 our knowledge of these important data to the palaeontologist. These, 

 so far as it was possible to do, have been explicitly stated in connection 

 with the descriptions in the following pages. 



It was our fortune at an early day, and during the progress of our 

 investigations, to interest and receive the earnest cooperation of a few 

 gentlemen, whose opportunities enabled them to furnish most important 

 data and material, all of which was generously placed in our hands. 

 Messrs. Frank Springer and Charles Wachsiiuth, of Burlington, 

 Iowa, have not only contributed large accessions in material, but it is to 

 Mr. Springer, and subsequently to Mr. Wachsmuth, that we owe the 

 discovery of the ichthyic horizon in the upper part of the Kinderhook at 

 that place, as well as some excellent explorations in the superincum- 

 bent Burlington formations, and Keokuk limestone, in south-eastern 

 Iowa. The interest which these gentlemen have evinced in the work, 

 and we may include as well that of others, and material aids which we 

 owe to them, render anything like an adequate acknowledgment of 

 their share of this important part of these investigations impossible in 

 so brief an accouut as the present. While these explorations in the 



