TELEOSTS. 263 



lateral line along the side of the back. Ammodytes, sand-launces, common 

 on sandy shores. 



SUB-ORDER 16. SCOMBROIDEA. 



Tail diphycercal, caudal usually strongly forked ; ventrals thoracic ; 

 scales usually small, cycloid, sometimes absent ; dorsal fin usually long. 

 A heterogeneous group, not easily defined; developing in three main lines. 

 SCOMBRID.E, head normal; spinous dorsal well developed; the dorsal 

 divided up into finlets. Scomber, mackerels, first appear in miocene; 

 Thynnus, horse-mackerel, tunnies (eocene) ; A uxis (miocene), frigate-mack- 



FlG. 262. Mackerel, Scomber scombrus. 



erel. TRICHIURID^E, body very long, tapering to a point; no caudal; 

 ventrals rudimentary or absent ; tropical. Trichiurus, cutlas-fishes. The 

 allied Lepidopus appears in the eocene. PALJEORHYNCHID.E, extinct. 

 XipHiiD^E, bones of upper jaw prolonged into a sword. Histiophorus, 

 sail-fish, possesses scales and teeth ; Xiphias, sword-fish, lacks both. Xi- 

 phiidids date from the upper cretaceous. 



CARANGID^E, pompanos of warmer seas ; caudal forked ; dorsal not 

 divided into finlets ; jaws normal. Naucrates, pilot-fish ; Seriola, amber- 

 fish (date from the eocene) ; Caranx, crevalles (miocene) ; Vomer and Selene, 

 moon-fishes, with greatly compressed bodies. Trachinotus, Platax, cre- 

 taceous. POMATOMID^E, blue-fish. CoRYPHjENiD^E. dolphins ; date from 

 eocene. STROMATEID/E, with teeth-like processes in the oesophagus ; 

 Rhombus, butter-fish ; Palinurichthys, rudder-fish. 



SUB-ORDER 17. GOBIOIDEA. 



Dorsal spines few and weak ; ventrals thoracic, usually close together ; 

 soft dorsal and anal long ; tail diphycercal. Over 600 species, mostly 

 marine, and of small size. Callionymus first appears in the miocene ; 

 Gobius (from eocene onwards) ; Clevelandia. Typhlogobuts of Californian 

 shores is blind. 



SUB-ORDER 18. DISCOCEPHALI. 



With the dorsal fin modified into a flat, transversly laminated oval 

 sucker on the top of the head; ventrals thoracic. Introduced by Opistho- 

 myzon in the eocene of Switzerland with a smaller sucker than in recent 



