AND ON THE CLASSIFICATION OF FISH. 523 
and description of their fossil forms, and which are of such a 
kind that this philosopher’s name must ever remain connected 
with the history of the Ganoids. As regards the subdivision 
of the living Ganoids, they are most naturally distributed as 
follows :— 
I. Houostet. 
Family 1. Lepidosteini. Genera Lepisosteus. 
ww». 2. Polypterini. ..  Polypterus. 
Il. CuyonpRostTEI1. 
Family 3. Acipenserini. Genera Acipenser, Scaphirhyn- 
chus. 
4. Spatularie. ..  Polyodon, Lacép., Pla- 
nirostra, Raff. 
The first have an osseous vertebral column, in the latter the 
skeleton is partly cartilaginous, and the vertebral column con- 
tains a soft chorda instead of vertebral bodies. Both are related 
to one another in the same manner as the Selachii and the Chi- 
mere among the Plagiostomi. 
Lepisosteus and Polypterus exhibit so many differences, both 
‘internal and external, that they cannot remain united in the 
same family. 
LepisosTEvs.—Its upper jaw is composed of several pieces. 
The vomer is double. The lower jaw contains as many pieces 
as in the Reptiles; its vertebre are articulated by articular ex- 
tremities and sockets*. The nose is situated at the extremity of 
the much-elongated jaw, and contains the ordinary nasal folds, 
which are arranged simply. It has a respiratory opercular gill 
as well as a pseudo-branchia, but no blowing-hole. The gills 
on the four gill-arches are perfect, 7. e. bifoliated, and behind the 
last arch and the hyoid bone there exists as usual a fissure. The 
gill-membrane passes over from one side to the other in the form 
of a mantle, is undivided, and contains three rays. The anterior 
margin of all the fins is covered with two rows of spinous scales. 
The fin-rays are all articulated. The caudal fin is abruptly 
truncate ; its rays are inserted partly at the posterior extremity 
of the vertebral column, partly beneath it. The stomach has no 
blind pouch. In the pylorus there are several short blind in- 
* The osteology of Lepisosteus is extremely well treated of by Agassiz in 
his Poissons Fossiles, t. ii. 
