ORDER CYCLOGAXOIDEA 37 



Order CYCLOGANOIDEA 



Skeleton bony; vertebra amphicoelous, as usual among fishes, the 

 anterior ones not modified; fins without spines; ventrals abdominal; a 

 mesoeoracoid; opercular skeleton complete; maxillary bordering mouth, 

 not transversely segmented; air-bladder cellular, lung-like, opening 

 into oesophagus. Fresh-water fishes of the United States and Canada. 

 A single living genus and family. 



Family AMIIDjE 

 (the bowfins) 



Oblong, subcylindrical fishes, compressed posteriorly, and with the 

 head bluntish and its external bones corrugated and very hard, scarcely 

 covered by skin; body covered with cycloid scales; skeleton bony; fins 

 without spines or fulcra ; dorsal fin long and low ; tail slightly heterocercal ; 

 gills 4. a slit behind the fourth; no spiracles; no pseudobranch and 

 no opercular gill; branchiostegals 10 to 12; opercular skeleton complete; 

 throat with two peculiar comb-like appendages of uncertain function; 

 nostrils double, the anterior with a short barbel; lateral line developed; 

 optic nerves forming a chiasma; jaws equal, the lower U-shaped, with a 

 bony gular plate between the rami; premaxillary not protractile; jaws 

 and palatines with strong conical teeth; vomer and pterygoids with 

 bands of small teeth ; stomach with blind sac; no pyloric caeca; intestine 

 with a rudimentary spiral valve; air-bladder cellular, bifid in front, 

 lung-like, connected by a glottis with the pharynx, and capable of 

 assisting in respiration. 



These fishes are remarkable for the simultaneous occurrence of 

 primitive ganoid characters — the cellular air-bladder, spiral valve, 

 gular plate, etc. — along with marked features of resemblance to the 

 modern is ispondylous forms (herring ami their allies) . The species 

 next described is the sole surviving representative of a once large 

 family, chiefly represented to-day by numerous fossils. TheAmiidcB 

 first appeared in the Upper Jurassic of France and Bavaria (genus 

 Megalurus), and fossilized remains of Amia occur in the Eocene 

 ><\ northern Europe and North America. The latter genus appar- 

 i ntly became extinct in Europe at the ch ise of the Lower Mil icene. 



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