346 M. Agassiz on Fossil Fishes. 



have appeared equally among fishes. This was the capital 

 point to establish. The fishes of the celebrated locality of 

 Monte-Bolca had, it is true, been referred by Volta, without ex- 

 ception, to species actually living in the Mediterranean ; but it 

 was easy to see that the determinations of the author of the 

 Ittiolitologia Veronese were not the result of sufficient study ; 

 many naturalists had pointed out his errors even by a simple 

 comparison of the plates. In order to be perfectly certain in 

 this respect, it was of importance to compare the originals 

 themselves. This M. Agassiz has done, with the greatest de- 

 tail, in the Museum of Paris, where the collection of Count 

 Gazzola, and the greater part of the originals of Volta's work, 

 are preserved. He was not long in discovering that all the 

 species were new, and that about the half belonged even to ex- 

 tinct genera. 



M. Agassiz has arrived at nearly the same results with re- 

 gard to the fossil fishes of another deposit, equally celebrated, 

 the species of which had also been regarded as identical with 

 those of our own times ; I mean the fishes of Oeningen. The 

 formation of Oeningen is a fresh-water deposit of more recent 

 date than Monte-Bolca. The fishes it contains are very similar 

 to those which now live in the Lake of Constance, and almost 

 all belong to the same genera. Now, when we consider how 

 little our Leucisci or poissons blancs differ from each other, we 

 might fear that the analytical method employed by Agassiz 

 would not be sufficient. Fortunately, the fishes of this locality 

 are in general admirably preserved, so well that we can study 

 the details of their skeleton with as much precision as that of 

 a living species. From the minute comparison our author has 

 made of these fossils with the fishes of the lake of Constance 

 and the basin of the Rhine in general, it appears that not only 

 are these fossils different from their living analogues, but also 

 that they equally differ from the fossil species of the other 

 great hydrographical basins, and in particular, from the species 

 of Menat in the basin of the Rhone. Now, in order that it 

 could happen thus, it is necessary to admit that at the period 

 of the deposition of these formations, the two basins of the 

 Rhone and the Rhine were already separated ; for if they had 

 communicated with each other, and if the fishes which now in- 



