MANUAL OF NATURAL HISTORY. 107 



3. FAMILY. True Sheat-Fishes (Siluridse). Body 



slightly elongate, compressed, generally slimy ; 



anal fin and tail long ; operculum moveable ; 



mouth furnished with cirrhi. 

 The genus Malapterurus possesses electric pro- 

 perties, but in a less degree than the Gymnotus or 

 Torpedo. 



4. FAMILY. Flat -Headed Sheat-Fishes (Aspredi- 



nidae). Eyes very small, vertical ; operculum 

 immoveable, the aperture opening only by a 

 a narrow slit beneath the head ; under jaw 

 transverse, and shorter than the upper ; first 

 pectoral ray generally excessively developed ; 

 dorsal single, close to head. 



5. FAMILY. Long-Headed Sheat-Fishes (Pterono- 



tidae). Head large, much lengthened, de-- 

 pressed, bony ; muzzle broad and obtuse, pro- 

 jecting beyond the lower jaw; cirrhi long; 

 dorsal fins two, the hinder generally adipose ; 

 caudal lobed or forked, rarely lunate. 



6. FAMILY. Double -Eyed Loaches (Anablepidaa) 



Body cylindrical, covered with stout scales ; 

 head small, short, depressed, not widened ; 

 eyes very prominent, apparently double ; 

 mouth transverse ; generation viviparous. 



7. FAMILY. Loaches -proper (Cobitidse). Body 



lengthened, slimy ; head Vith cirrhi ; mouth 

 inferior ; teeth none ; gill-opening small ; 

 dorsal fin central, above the ventral. 



8. FAMILY. Thick - bodied Loaches (Poeciliidse). 



Body thick, oval, compressed ; scales large ; 



