28 FISH GALLERY, 



In the fishes of Group A an anal fin is present between the 

 cloaca and the tail fin, and there is a tendency for the spiracle to 

 become reduced in size. The vertebral centra are astero-spondylic, 

 i. e. if viewed in transverse section they are seen to be strengthened 

 by calcified ridges or radiating laminae which predominate over the 

 concentrically disposed laminae (compare the asterospondylic 

 vertebras of Cestracion (20) and Scyllium (28) with the tecto- 

 spondylic vertebras of Rhina (90, Wall-case 2). Group A 



Fig. 14. — Upper jaw of Port Jackson Shark, Cestracion p/nlippi. 

 (From Giinther, " Study of Fishes.") 



includes the families Cestraciontidae, Cochliodontidae, Scylliidae, 

 Lamnidae, Rhinodontidae, and Carchariidae. 

 Port In the family Cestraciontidae, the best-known example of which 



Shark * s tfte ^ ov ^ Jackson Shark (24), each of the two dorsal fins is 

 armed with a stout spine (see spine, 24 a), and the first dorsal fin 

 is opposite the space between the pectoral and pelvic fins. The 

 nasal and buccal cavities are confluent ; there is no nictitating 

 membrane ; the teeth, except those at the front of the mouth, are 

 blunt, and adapted for crushing the shells of molluscs and 

 crustaceans (see jaws, 19, and fig. 14). Sharks of this family 



