204 ZOOLOGY SECT. 



nearly homocercal. The pelvic fins are abdominal. A reduced 

 spiral valve, a conus arteriosus, and an optic chiasma are present. 



This order includes the Gar-pike or Bony Pike (Lepidosteus, Fig. 

 825), from the fresh waters of North and Central America and 



Pety 



FIG. 826. Amia calva (Bow-fin). A, the entire animal; B, ventral view of throat, br.m. 

 branchiostegal membrane; c. f. caudal fin; d. f. dorsal fin; jurj. pi. jugular plate; pet. j. 

 pectoral fin ; pv. f. pelvic fin ; v. /. ventral fin. (After GUuther.) 



Cuba, and the Bow-fin or Mud-fish (Amia calva, Fig. 826), from the 

 rivers of the United States. 



Orders 1 3 are frequently grouped together as the sub-class 

 Ganoidei, and, although such a group is an artificial one, it will 

 often be convenient to refer to these fishes as " Ganoids." They 

 are all small arid numerically insignificant groups at the present 

 day, but formed the whole of the Teleostomian fauna in the 

 Palaeozoic and the greater part of the Mesozoic epoch (vide 

 infra). 



ORDER 4. TELEOSTEI. 



Teleostomi in which the paired fins have no basal lobe. The 

 skull is well ossified both by cartilage and membrane bones : 

 branchiostegal rays are present. The vertebral column is well 

 ossified : the tail is homo- or diphycercal. There is no spiral 

 valve, except as a vestige in one genus. The conus arteriosus is 

 absent except as a vestige in one genus : a large bulbus aortse is 

 present. The optic nerves never form a chiasma and usually 

 simply decussate. 



The vast majority of existing Teleostomi are included in this 

 order, which is divided into six sub-orders as follows : 



Sub-order a. Physostomi. 



Teleostei in which the air-bladder, when present, has an open 

 pneumatic duct. All the fin-rays are jointed, and the pelvic fins, 

 when present, are abdominal in position. 



