AND ON THE CLASSIFICATION OF FISH. 509 
The grounds which should determine the removal of the above 
families from the Ganoidei, apply equally to the Lepidosiren, 
which was appended to the Ganoidei, from which it differs as 
much by the valves of the dulbus arteriosus as by the structure 
of its scales. Agassiz ascribes a layer of enamel to these scales ; 
but in their mosaic structure they approach the compound 
scales of Sudis and Osteoglossum. They have no concentric 
raised lines, and are merely granulated aud reticulated on the sur- 
face ; but such elevated lines in the scales of osseous fishes im- 
perceptibly pass into reticulations and granulations, as may be 
seen in the free portion of the scales of Sudis and Osteoglossum. 
I have never been able to find any enamel on the scales of the 
Lepidosiren. 
I shall now turn to another important point in the organiza- 
tion of the Ganoids, the respiratory organs. 
In my treatise on the accessory gills and pseudo-branchiz, I 
have proved that the false accessory gills or pseudo-branchiz 
with the function of a rete mirabile occur in the osseous fishes, 
as well as in the Plagiostomi and Sturiones; that, on the other 
hand, a true accessory gill, anterior to the first gill-arch, near 
the operculum, does not appear in any osseous fish, and charac- 
terizes the Sturgeons, which have this in common with the 
Plagiostomi, although in the Plagiostomi the operculum is 
wanting. It was also there pointed out, that the Sturgeons 
possess both the true accessory opercular gill and the pseudo- 
branchiz, the latter existing in the blowing-cavity. This pro- 
perty of possessing a respiratory opercular gill is not peculiar 
to the Sturgeons as Sturgeons, but, as will now be shown, so far 
as they are Ganoids; for the Ganoids differ in this character 
from the osseous fishes, and approach the Plagiostomi, as they 
do also in the structure of the valves. 
The intimate relation of the Sturgeons with the Ganoids re- 
mained long concealed from me, and I had not understood it, 
even at the time when I detected the numerous valves of Polypte- 
rus, as is evident from my report on Agassiz’s Poissons Fossiles 
in the last Jahresbericht; for I then possessed the means of 
separating the Sclerodermi, the Gymnodontes, Siluroidei, Go- 
niodontes and Lophobranchii from the Ganoids; but the Stur- 
geons then appeared to me to be distinct from the Ganoids. 
This was necessarily established in the complete development of 
my ichthyological inyestigations. Thus in making observations 
