227 



A Classification of the Class Pisces (Fishes). 



With Examples and Notes. 



gjlb-class r,TTmvr>TtTnTTTHVF.p. Cartilaginous fishes, without true bone. \ 

 A spiral valve in intestine. Without an air-bladder. Gut, and 

 urinary and genital ducts open into a common cloaca. A conus. 

 Tail generally heterocercal. Paired fins of ichthyoptergyium 

 type. (See page 194). Pelvic fins of male have claspers. Ova 

 few and large, and fertilisation internal. 



Order Elasmobranchii or Selachii. Skin has placoid scales. 

 Vertebral column is segmented. Skull generally hyostylic. 

 Five to seven pairs of gill-clefts (separated by complete 

 septa) ; also spiracles, frequently. Without a complete 

 operculum. Without a larval stage. 



Sub-order Selachoidei (Sharks, Dogfishes). Body elongate 

 hded. 



and. roun 



Examples, Chlamydoselachus. Mouth anterior. 

 Nostrils lateral. Six pairs of gill- 

 clefts. 



Scyllium (Dogfish). (See pages 219 to 

 226.) 



Mustelus. Viviparous. A placenta- 

 like connection between uterus of 

 mother and yolk-sac of embryo. 



Carcharodon (Man-eating Shark). 



Selache (Basking Shark). 



Acanthias, syn. Squalus (Spiny Dog- 

 fish). Viviparous. 



(^Sub-order Batoidei (Skates, Rays). Body flattened. Pec- 

 toral tins confluent with head region. 



Examples, Pristis (Saw-fish). Snout produced as 



a long rostrum with saw-like teeth. 

 Torpedo. With electric organs between 



pectoral fins and head. 

 Raia (Skate). (See pages 219 to 226.) 

 Has electric organ in tail region. 



Order Holocephali. Skin is without placoid scales. Vertebral 

 column is not segmented. Skull protosytlic (autostylic). 

 Four pairs of gill-clefts, covered on each side by a fold, 

 the operculum. Without spiracles. 



Example, Chimaera. 



Sub-class OSTEICHTHYES (Bony Fishes) or TELEOSTOMI. Skeleton 

 more or less ossified (true bone). Skull hyostylic. Mouth 

 usually antero-terminal. Without a cloaca. There is generally 

 an air-bladder. A gill-cover or operculum on each side. The 

 gill septa are greatly reduced. Without claspers. Ova small 



