526 MULLER ON THE STRUCTURE OF THE GANOIDS, 
and Cuvier, united them with the Cyclostomi and Plagiostomi to 
form a large section of the Chondropterygii. 
The difference of the osseous or partly cartilaginous skeleton 
is of but little importance when applied to the order of the Ga- 
noids, as is evident from Agassiz’s fossil Ganoids. But in sub- 
dividing the Ganoids, it appears to me to be very important ; 
at least it is so with the Selachii. For the Sharks and Rays, 
in which the vertebre are perfectly divided, and the Chimere, 
in which there is a chorda dorsalis, form groups which are in 
other respects remarkably distinct, although they are inseparable 
from the Selachii. In a treatise on the vertebral column of the 
Plagiostomi, which was undertaken for Agassiz’s Poissons Fos- 
siles, and is published in the second volume of that work, I 
have pointed out others which have a soft cartilaginous vertebral 
column in addition to the Sharks, which possess an osseous 
vertebral column. In them these cartilaginous bodies of the 
vertebrz are separate in the column of the spine, and the chorda 
is wanting; but the Chimere, on the contrary, really possess a 
true chorda. 
The Acipenserini and Spatularie are principally distin-— 
guished by the skin, which is naked in the latter, and by the 
formation of the mouth, the jaws, and the opercula*, Opercula 
are also absent in the Spatularie (Planirostra). Their intestines 
are the same. 
In the scales, the fossil Ganoids have more similarity to the 
living Holostei than to the Sturgeons; however, in the structure 
of the osseous or partly cartilaginous vertebral column, the 
former and the latter forms recur; it is difficult to arrange them 
among the living forms, because we are obliged to mix the posi- 
tive facts of the anatomy of the living forms with those partially 
suspected of the fossil. In addition to Lepisosteus, according to 
Agassiz, we find numerous Lepidoid and Sauroid forms, which 
resemble it in the structure of the fins, having two rows of fulcra, 
and also in the completely ossified vertebral column, as Lepidotus, 
&c. But I am not acquainted with any analogue of Polypterus 
among all the fossil Ganoids, so that it appears to be even among 
them the type of a peculiar family. I consider the Celacanthi, 
Pycnodontes, and the families of the Cephalaspides, Acanthoidei, 
and Dipteri, which have been lately formed by Agassiz, as 
well-marked families, excepting perhaps the placing Cheirolepis 
* See my Vergl. Osteologie d. Myxinoiden. 
