220 ZOOLOGY sect. 



Cuba, and the Bow-fin or Mud-fish (Amia calva, Fig. 875), 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 and 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. 



Order 4. — Teleostei. 



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

 skull is well ossified both by replacing and investing 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 a small number of genera : 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 : — 



Suh-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 



Pig. 876.— Rita buclianani, one of tliD Siliiroids. b. barbel ; d.f. r. 1, first dorsal fin-ray ; 

 d. J. 3, adipose fin ; pet. /. r, 1, first pectoral fin-ray ; pv. f. pelvic fin ; v. /. ventral fin. 

 (After Day.) 



the pectoral are armed each with an anterior ossified spine, and 

 the pelvic fins, when present, are abdominal in position. 



Including the Cat-fishes or Siluroids (Fig. 876), Carp, Gudgeon, 

 Loach, Pike, Salmon and Trout (Fig. 854), Smelt, Grayling, 

 Herring, Anchovy, Eels, &c. 



