GEN. PTER0MY20N. LAMPREY. 339 



themselves from the exertion necessary to prevent 

 them being carried down by the current. To this 

 habit the name of Lamprey is supposed to refer, its 

 probable derivation being from lamhendo petras ; 

 and it corresponds to the term Pteromyzon, which is 

 composed of two Greek words of nearly the same 

 import. With the exception of the two first spe- 

 cies noticed below, they are small fishes of no com- 

 mercial importance ; but they are full of interest to 

 the naturalist, as occupying the low^est place in the 

 scale of organization, not only of their own class^ 

 but, perhaps, of all vertebrate animals, and showing 

 the gradual approaches which one class of animals 

 make to another. 



Gen. CXXII. Pteromyzon. — The circular mouth 

 and seven apertures in the side of the neck, are two 

 characters sufficiently distinctive of this genus. The 

 fin, which runs along the posterior portion of the 

 back and tail, can scarcely be regarded as a true fin, 

 as it is merely a fold of the skin, and quite destitute 

 of rays. 



(Sp. 148.) P. marinus. The Lamprey. This, 

 the most conspicuous and best known member of 

 the family, bears some resemblance in its genera\ 

 appearance to the Mura?na formerly noticed. It 

 measures from two to three feet ; the body thick 

 and cylindrical ; the colour yellowish brown or 

 tinged with green, and marbled with dusky. It is 

 frequently found in all the principal rivers of the 

 three kingdoms, being particularly abundant in the 

 Severn, and has a very wide range throughout Eu- 



