8 



Guide to the British Fresh- Water Fishes 



thoracic, below the pectorals. In the Trout all the fin-rays are 

 tiexible, jointed and branched ; in the Perch some of the rays 

 are stiff pointed spines. 



pmx 



J3mx 



Fig. 1.— Diageammatic Figures of Perch (A) and Trout (B). 



jpmx, praemaxillary ; mx, maxillary ; op, operculum ; d, dorsal fin ; d', spinous 

 dorsal fin ; d", soft dorsal fin ; ad, adipose fin ; c, caudal fin ; a, anal fin ; 

 pv, pelvic fin ; p, pectoral fin. 



PETEOMYZONIDAE. 



This family includes about twenty species from the coasts and 

 rivers of all temperate regions ; some of these feed in the sea, but 

 all breed in fresh water. 



The Lampreys resemble Eels in form, but differ from them 

 widely in structure ; the most notable external differences from 

 other fishes are that the mouth is surrounded by an expanded 

 circular lip, the suctorial disc, which bears horny teeth, and that 

 there is a series of seven small gill-openings on each side. There 

 are no jaws, but there is a very muscular protrusible tongue, also 

 furnished with horny teeth. 



Lampreys attach themselves by means of the suctorial disc to 

 other fishes and devour them, sucking the blood and scraping off 



