THE FAMILY OF " ROUND-MOUTHED" FISH. 413 



mouth, as already explained, performs the functions of a 

 sucker ; but in the young it has the form of a horse-shoe, 

 the lower edge of the circle being not sufficiently deve- 

 loped for the purpose of suction ; the teeth are unformed, 

 and there are other remarkable structural differences. It, 

 therefore, has not the power of attaching itself to stones, 

 &c., like the adult Lampreys, but usually buries itself in 

 the mud or sand at the bottom of rivers and brooks, in 

 most of which it will be discovered upon close search. Its 

 length seldom exceeds 6 or 7 inches, and its thickness is 

 about equal to that of a large quill : the most common 

 colour is yellowish brown, approaching somewhat to black 

 on the top of the head and upper part of the back, getting 

 much lighter underneath and on the fins. 



These small Lampreys make excellent bait for eels and 

 for some species of sea-fish. 



The vignette shows the arrangement of the parts con- 

 cerned in the respiration of the common or Sea- Lamprey, 

 reduced from Plate 11, Philosophical Transactions, 1815. 



