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 chiefly 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. 



