PERCH TRIBE. 



337 



jaws are of small and uniform size; and teeth are present on the vomer and 

 palatine bones. The anal fin has but a single spine ; although the margin of the 

 propercular bone is serrated, that of the preorbital is smooth ; and the scales are 

 small. These fishes inhabit the Danube and certain other European rivers. 



Under this name, which belongs properly only to the British 

 form, may be included a few small perches, of which the typical 

 representative (Acerina cernua) is shown in the lower figure of the annexed illus- 



Ruffes. 



LARGER AND SMALLER DANUBIAN PERCHES, AND RUFFE (J liat. size). 



tration. From the other members of the family this and the allied genus Percarina 

 differ by the large size of the slime cavities on the sides and top of the head ; the 

 ruffes being specially distinguished by the dorsal fin being undivided, and also by 

 the maxilla being covered by the preorbital bone. The fishes of this genus have the 

 body somewhat low, and the scales somewhat small ; the continuous single dorsal 

 fin carrying from thirteen to twenty -nine spines ; and there being two spines in 

 the anal fin. There are no tusks among the small teeth of the jaws, and the 

 tongue and palatine bones are devoid of teeth, although these are present on the 

 vomer. The genus is confined to the cooler portions of the Northern Hemisphere, 

 VOL. v. 22 



