103 

 KEY TO THE ORDERS AND FAMILIES. 



PRIMARY DIVISIONS. 



1. Fishes with a bony skeleton. 



Gills free, with one opening on each side ; caudal symme- 

 trical, or absent. Teleostei. 4. 

 „ Fishes with a membranous or cartilaginous skeleton. 

 Gills attached, with several openings. 2. 



2. Skeleton cartilaginous. 3. 

 „ Skeleton membranous. 



Eye rudimentary ; mouth a longitudinal fissure. Lepto- 



CARDII. 67. 



3. Body eel-like ; mouth circular, suctorial. Cyclostomata. C7. 

 „ Body shark-like ; caudal unsymmetrical. Chondrop- 



terygii. 9. 



NATURAL ORDERS. 



4. All the fin rays soft, articulated.* 5. 



„ Portion of the fin rays spinous, not articulated. 8. 



5. Gill-openings more or less wide, one on each side ; body 



scaly or smooth. 6. 

 „ Gill-openiiigs reduced to narrow slits, usually situated in 

 front of i)ectoral fins ; body with osseous rings, or skin 

 covered with scutes or spines ; never scaly. 7. 



6. Ventral fins, if present, jugular or thoracic. Anacaxthixi. 



41. {Type^ Flounder.) 

 „ Ventral fins, if present, abdominal. Physostomt. 44. 

 {Types^ Salmon; Herring.) 



7. Gill-cover reduced to a large simple plate ; body composed 



of osseous rings. Lophobranchii. 52. {Type^ Sea 

 Horse.) 

 „ Gill-opening a narrow slit in front of pectorals ; body with 

 rough scutes or spines. Plectogxathi. 52. (Types^ 

 Leather Jacket ; Toad Fish.) 



8. Inferior i)]iaryngeal bones separated. Acaxthopterygii. 



10. C^\i/pc^ Trmnpeter.) 

 „ Liferior pharyngeal bones coalesced with or witliout a 

 median longitudinal suture. Acaxthopterygii-Pha- 

 RYXQxoGXATiii. 53. {Type^ Parrot Fish.) 



9. External gill-opening, one covererl l>v a fold of the skin , 



jaws coalescent witli the skull. "Holocephala. 54 

 {Tyjie, Elephant Fish.) 

 „ External gill-openings five to seven ; jaws distinct from 

 skull. Plagiostomata. 55. {Tyjjes, Hammer Shark : 

 Dog Fish; Skate.) 



» 111 this group 13 included certain iislios, like llic fcalmou, wUociC tlrst ray of 

 dorsal and pectoral la sometimes more or less ossified. 



