xni 



PHYLUM CHORDATA 



213 



homocercal. The pelvic fins are abdominal. A reduced spiral 

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



FIG. 885. Lepidosteus platystomus (Bony Pike), c./. caudal fin; d. f. dorsal fin; 

 fl. fulcra ; 1. I. lateral line ; pet. f. pectoral fin ; pv. f. pelvic fin ; e. /. ventral fin. (After 

 Cuvier.) 



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

 Fig. 885), from the fresh waters of North and Central America and 

 Cuba, and the Bow- B 



fin or Mud-fish (Amia 

 calva, Fig. 886) 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 FIG. 886. Amia calva (Bow-fin). A, the entire animal ; B, 



if \vill nffon V>o ventral view of throat, br. m. branchiostegal membrane ; 



le > ] c. f. caudal fin ; d.f. dorsal fin ; jug. pi. jugular plate; 



Convenient to refer fct. f. pectoral fin ; pv. /. pelvic fin ; v. f. ventral fin. 



, (After Giintlier.) 



to these fishes as 



" Ganoids." They are all small and numerically insignificant 



groups at the present day, but formed the whole of the Teleosto- 



mian fauna in the Palaeozoic and the greater part of the Mesozoic 



epoch. 



ORDER 4. TELEOSTEI. 



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

 skull is well ossified both by replacing and investing bones : branchi- 

 ostegal rays are present. The vertebral column is well ossified : 

 the tail is homo- or diphy cereal. There is no spiral valve except 

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

 as a vestige in a small number of genera : a large bulbus aortae 

 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, or the dorsal and 



VOL. II O 



