22 ACIPENSERIDJE. 



frontal plate is composed of six pieces, and the squamosals 

 are not united to either the mastoids or temporals. The 

 reason for entertaining a doubt of the identity of the 

 species is the difference of character of the surface of 

 both cranial and body-shields. In the small specimen 

 the roughness of the plates is produced by round grains of 

 various sizes disposed in radiating lines with furrows be- 

 tween, while in the old the crenulated .edges of the thin 

 walls that bound the depressions do not rise above the 

 general level. The osseous centres form in the young 

 thin crests, which on the dorsal shields have a hooked 

 apex. A continuous crest runs from the centre of the 

 temporal along the side of the head to that of the mas- 

 toid ; and owing to the greater elevation of the centres 

 of the coronals the mesial trough is deeper than in the 

 larger fish, but the lines which in the latter form the pro- 

 file of an obelisk are not evident. The suprascapular is 

 pitted with radiating grooves towards its edges, and the 

 coracoid is also decidedly radiated. The skin between 

 the rows of body-shields is studded with roundish, irre- 

 gular, very small osseous grains, the larger ones being 

 radiated on the edges. In the recent state this radiation 

 would be concealed by the epidermis. The barbels are 

 short, tapering, and more remote from the tip of the 

 snout than in larger fish. An under caudal lobe is al- 

 ready formed. The body-shields number fourteen on the 

 dorsal row ; thirty-eight on the right side in a line with 

 the suprascapular, and forty on the left side ; eleven 

 ventral ones on the right side, and ten on the left. The 



fin-rays are 



D. 37 : V. 27 : A. 26. 



The osseous centres of the coronals and temporals are 

 equidistant from the tip of the snout. 



The following wood-cut, reproduced from the first 



