44 
covered. By the information thus acquired, it is possible to determine whether a 
fish inhabited river, lake, or pond, the open sea, or the shallow waters ; whether 
it lived on the surface, or frequented the great depths. These indications may 
serve to determine divers important circumstances in the formation of rocks. 
Another peculiar advantage resulting from the study of Fossil Fishes is, that 
the examination invariably makes us acquainted with the whole organization, and 
affords a perfect idea of its pristine condition. Such researches must consequently 
lead to results much more satisfactory than the study of the Mollusca , of which 
only the shells have been preserved ; and more general than that of the Mammi- 
fera , the whole skeleton of which is rarely discovered, and that only in the most 
recent strata. The Reptiles, even when more generally known, can scarcely emu¬ 
late the fishes in importance : since they are of rarer occurrence, and were deve¬ 
loped at a later period in the series of creations. 
Fossil Fishes differ according to the great geological formations in which they 
are found; and exhibit, in each, a peculiar character of organization sufficient for 
their determination. They differ the more widely from the fishes of the existing 
period, as they are found in formations of a more ancient date. All the bony 
fishes anterior to the chalk, are referrible to genera, which have no longer repre¬ 
sentatives in the present world: they are invariably characterized by rhomboidal 
scales covered with enamel. Those of the same formations, which, in the present 
System, would be associated with the Chondropterygii , possess, like the genus 
Cestracio , flattened, dotted, or differently plaited teeth. 
Comparisons thus multiplied, justify, in the opinion of the Professor, an alte¬ 
ration in the arrangement of Fishes ; which will frequently indicate affinities 
hitherto unknown: and the new classification, which he advocates, is intended to 
expose the whole of the natural relations of fishes with each other, and their suc¬ 
cession in the series of formations. General geological considerations, moreover, 
drawn from the study of these fossils, will exhibit the connection which exists be¬ 
tween the organic development of the earth, and that of the different Classes of 
animals. These ideas will be completed by the organic representation of each of 
the great geological periods. 
Great pains have evidently been taken, by Professor Agassiz, in examining 
the various organs of fishes found in a fossil state, and in discovering the charac¬ 
ters proper for their distribution into families, genera, and species. With this 
view, he has applied himself, in an especial manner, to the study of the skeleton 
of fishes, and to the microscopic inspection of several thousands of scales belong¬ 
ing to more than two hundred species of different genera and families. 
As regards the publication of the work, the first volume will be devoted to an 
examination of all the general questions. It will contain an Introduction to the 
study of Fossils ; an indication of the sources from which the Professor has 
drawn, in the prosecution of his researches ; and the general anatomy of the 
