l\OLL CALL jy^ 



Class I — Elasmobranchii — Gristle-fishes {Sgualus, Raia). 



Characteristics: Cold-blooded fishlike vertebrates witli jaws; charac- 

 terized by a cartilaginous skeleton, i)(>rsistent notochord and placoid scales; 

 upper jaw suspended to ci-aniuin indirectly by means of ligaments and 

 cartilages (hyostylic). 



Class II — Holocephali -^ Elephant-fishes (Chimaera). 



Characteristics : Immovable upper jaw fused with cranium (autostyiic) 

 resembling higher forms; gill slits covered by flap (operculum); tail 

 heterocercal. 



Class III — Ganoidei — Enamel-scaled fishes (Acipenser, Lepisosteus, Polyp- 

 terus). 

 Characteristics : More or less armored fish ; remnants of group dominant 

 in Devonian seas; degenerating spiral valve in intestine associated with 

 presence of pyloric caeca; scales usually rhomboidal, fitting together 

 rather than overlapping; dorsal fin usually close to caudal fin. 



Class IV — Dipnoi — Lung-fishes (Neoceratodus, Lepidosiren, Protopterus). 



Characteristics: Semitropical fishes, passing dry season by aestivating in 

 slimy cocoon ; during period of active life use gills, and while aestivating 

 breathe air, the modified swim bladder acting as a lung; cycloid scales; 

 auricle of heart partially divided. 



Class V — Teleostei — Bony fishes (Ctenolabriis, Perca, Gadus, Microptcrtis). 

 Characteristics : Bony fishes, breathing primarily by gills ; well-develoiM-d 

 operculate bones, cycloid or ctenoid scales ; tail homocercal. These fishes 

 constitute about 90 per cent of all known varieties. 



