262 



CLASSIFICATION OF VERTEBRATES. 



SUB-ORDER 12. SQUAMIPINNES. 



Ventrals thoracic, tail diphycercal ; scales small, ctenoid ; dorsal fin 

 long, scales upon the soft portion ; postorbital usually ossified to the skull. 

 The squaniipinnes have left the main stem somewhere near the point of 

 differentiation of percoid and scombroid groups. In turn they have given 

 rise to the plectognaths. The order is introduced by Pomacanthus, and 

 Asineops in the eocene. In the CH^TODONTID/E the teeth are bristle-like 

 and thick set. Chcetodon, butterfly-fishes ; Holacanthus, emperor-fishes ; 

 Toxodon, the archer fish, has the palatines with teeth. All the forms are 

 tropical or subtropical. TEUTHID^:, doctor-fishes, teeth incisor-like ; 

 caudal peduncle is armed with spines or plates, and frequently becomes an 

 important weapon of defence. Teuthis, tropical seas. 



SUB-ORDER 13. PERCESOCES. 



Ventrals abdominal, spined ; dorsal spines few, usually forming a sepa- 

 rate fin, tail diphycercal, third superior pharyngeal enlarged, scales cycloid. 

 The percesoces form another stem, arising probably from the ancestors 

 of the hemibranchs and lophobranchs, and close to the synentognaths. 

 In turn the scombroids have descended from some percesocid form. ATH- 

 ERINID^E, or silver sides, lateral line lacking, teeth small or wanting; 

 head and body elongate; species carnivorous, mostly marine; Atherina 

 (appears in eocene) Menidia. MUGILID^E, mullets, herbivorous ; differ 

 from last in the short and broad head. Mugil dates from oligocene. 

 SPHYR^ENID^E, lateral line distinct; teeth strong. Sphyrcena, the barra- 

 cudas of warmer seas. Scyllcemus, cretaceous. The OPHIOCEPHALIDVE 

 of the rivers of India belong near the percesoces, but differ in absence 

 of spines from all fins. They are capable of aerial respiration, and lead 

 to the labyrinthici. The tropical POLYNEMID^E show some relationships to 

 the mugilidae. Polydactylus. 



SUB-ORDER 14. LABYRINTHICI. 



Dorsal and anal spines present, ven- 

 trals thoracic, lateral line interrupted or 

 absent ; a complicated apparatus of bony 

 laminae supporting a respiratory mem- 

 brane in the accessory branchial cham- 

 ber, by means of which the animal can 

 breathe air. All are tropical. Anabas 



FlG. 261. Head 



Anabas, 



showing the labyrinthicine apparatus, is sai d to climb trees. Osphromenus, the 

 after Zograff. gouramy. 



SUB-ORDER 15. AMMODYTOIDEA. 



Ventrals absent, no spines in any fins, in other respects much as in the 

 percesoces. A group of uncertain relations, placed here for want of a 

 better place. A single family, AMMODYTID^:, with cycloid scales, no teeth, 



