294 
CARTILAGINEI. — ACIPENSERID^. 
rays. The gill-plate, being furnished with a 
membranous margin, can close the aperture so 
accurately as to exclude water, and even air. 
The body is long, and tapering gradually to the 
tail, which is furnished with a caudal fin of re- 
markable structure. It is unequally forked, the 
upper lobe being considerably the longer ; but 
this is not the only difference, for (as in the 
Shark, which exhibits the same form of the cau- 
dal,) the upper lobe is penetrated by the ter- 
minal joints of the spinal column, which run 
through its centre to the extremity; the lower 
lobe is formed only of rays’. The body and the 
head are covered with large bony plates, those on 
the head of various angular forms, fitting into 
each other, those on the body arranged in longi- 
tudinal rows, with their centres rising into spines 
pointing backwards. The mouth, situated be- 
neath the head, is small and toothless ; it is 
placed on a sort of foot of three joints, by means 
of which it is capable of considerable protru- 
sion. 
These are fishes of large size, some, indeed, 
attaining gigantic dimensions ; they inhabit rivers, 
lakes, and inland seas, and chiefiy in the northern 
regions of the globe. They migrate at certain 
seasons to the sea, but deposit their spawn in 
freshwater. Twenty-four species are enumerated 
by the Prince of Canino as belonging to the 
Family, including one or two singular species of 
North America, which, with most of the charac- 
ters above-mentioned, have the snout prolonged 
into a broad, leaf-like, bony plate. 
