INTKODUCTION. 
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■which cannot always be identified with much certainty or precision. 
The Catalogue of the extinct Acanthopterygii is thus, for the most 
part, a bare list of names of fragmentary fossils, to which an 
approximate and provisional systematic position has been assigned. 
This circumstance is all the more regrettable, since no satisfactory 
classification of the surviving Acanthopterygii has hitherto been 
proposed, and the aid of Palaeontology is much needed for its 
accomplishment. 
Axacanthixi. 
Typical cod-fishes and flat-fishes date back to the Oligocene and 
Upper Eocene periods respectively. No generalised ancestors of 
either type have hitherto been recognised. 
'With fragmentary materials of this nature, it is impossible to 
attempt a very exact classification. It has, therefore, been deemed 
advisable to adopt a broad conception of families and genera more in 
accordance with that of Ur. Gunther than with that of later writers. 
This corresponds with the method of treatment followed in the 
earlier parts of the Catalogue, and still seems adequate for a 
s}Tioptical work of which the results can only be provisional. Lists 
of the specimens in the Museum and the published names of fossils 
not represented in this collection have been arranged approximately 
in their natural order for convenience of reference, without any 
detailed discussion of their affinities. The incorporated new matter, 
indeed, relates rather to the facts of osteology than to premature 
essays in taxonomy. A detailed knowledge of the skeleton of the 
early bony fishes of the Cretaceous period is particularly important; 
and the writer has made special efforts to discover the essential 
facts by studying most of the available collections. He is indebted 
to the Lev. William Eird and Professor Alfred Ely Day for the 
opportunity of examining the fine series of Cretaceous fishes from 
Mount Lebanon in the Syrian Protestant College at Peyrout; to 
Professor Karl Busz for permission to study the unique collection of 
Westphalian Cretaceous fishes in the Academy of Munster; and to 
Professor S. W. Williston, for the privilege of making a detailed 
examination of the remarkable remains of fishes from the Kansas 
Chalk, now in the Museum of the State University of Kansas. A 
brief survey of the Cretaceous fishes from Northern Brazil in the 
