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. 
Ruffes 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- 
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 
