410 THE FRESH- WATER FISHES (F El'ltOI'E. 



As might be expected from the wide geographical distribution and diverse 

 habitat of this species, it is extremely variable, and its synonymy is, on this 

 account, difficult to disentangle. Indeed, any one who should critically com- 

 pare the figures of the species given by modern naturalists might well hesitate 

 to regard them as representations of the same kind o fish ; but, like other 

 Sturgeons, this type varies with age, and the long pointed snout of the young, 

 which, as usual, curves upward, becomes replaced by a broader, shorter snout, 

 in which the curvature is lost. The body is, at first, pentagonal in section, but 

 the surfaces between the rows of scutes afterwards become filled out and 

 rounded. The lower lobe of the caudal fin, which is at first absent, develops 

 with age. The unjointed rays of the pectoral fin subsequently become jointed. 

 Certain differences may be observed in the shields of the body and the head, 

 as may be seen by comparing the figure of a fresh head (Fig. 200) with the 



Fig. 199. ACIPENSEK STU1UO 



dried head figured by Yarrell, differences sufficiently obvious to have induced 

 Sir John Richardson to describe the British Sturgeon as a distinct species. 

 Probably no work would throw more light upon the nature of species than a 

 thorough investigation of the variability of Acipenser stnrio. 



In form of body (Fig. 199), and length and shape of snout, this species 

 most resembles A. ginnlmi. The height of the body over the pectoral fins 

 exceeds the thickness by one-third, so that the section is vertically ovate, and 

 the aspect of the fish slightly compressed. The head is as wide as the body 

 is high, and this measurement is one-eighth of the total length. The head is 

 two-ninths of the length of the fish, but in the young it is one-quarter of the 

 length. The extremity of the snout seen from above is triangular. The 

 profile rises with a gentle convexity to the back of the head. 



The shields which cover the head are rather roughly granular than radiated, 

 and in close contact (Fig. 200). The first dorsal shield is only slightly wider 

 than the supra-occipital. The latter is T-shaped, with both the transverse por- 

 tions and anterior stem broad. An anterior denticle from the keel of the first 

 dorsal scute penetrates a little into the supra-occipital. The epiotic shields 

 are parallel and long. They reach a little farther forward than the supra- 



