160 COMMON STURGEON. 



in the more prominent parts there is some approach to regu- 

 larity, on the whole this may be even the least depended on. 

 Not only do the different varieties differ in this respect, but 

 the variation exists in the same individual; so that a cord, 

 laid along the middle line from the top of the head to the 

 snout, shall sometimes separate the sides into portions which 

 do not answer to each other. 



With regard to the plates on the back, Linnaeus, in his 

 specific character of this fish assigns to it a row of eleven 

 plates along the dorsal ridge; wdiereas Willoughby tells us 

 that he had counted from eleven to thirteen in several different 

 examples; and particularly he mentions that behind the single 

 dorsal fin there were no dorsal plates, where in most figures 

 they are represented; and in the specimen presently to be 

 described this portion of the body was ornamented and de- 

 fended by a pair of parallel rows. Several other variations of 

 figure might be brought forward, but I judge sufficient has been 

 said to shew that the division of this well-known Common 

 Sturgeon into two species has a less certain foundation in 

 nature than has been supposed. 



Our description of this fish is taken from an example kindly 

 presented by William Thompson, Esq., of AVeymouth, whose 

 desire to extend the boundaries of science has shewn itself 

 in similar instances on many former occasions. In this instance 

 the obligation is so much the greater that it has enabled me 

 with more ease, and at longer intervals, to examine the 

 minuter particulars of form and structure, than if I had been 

 limited to an inspection of what was exhibited in the boat of 

 a fisherman, or a fishmonger's shop. 



The example described measured three feet seven inches in 

 length. The head at top is depressed into a wide channel, 

 with the ridges on the sides more prominent; it slopes gradually 

 to the snout, which becomes almost sharp at the end, where 

 it is slightly bent up. This surface, and also the sides of the 

 face, are formed of a bony crust which is divided into sections; 

 but when first from the water these divisions can scarcely be 

 made out, and it is only when the surface has become 

 dry that those plates can be distinguished, which have been 

 represented in drawings of those parts. An elevated prominence 

 stands before each eye. The plates are more numerous, smaller. 



