ASTYLOPTERYGIAN FISHES. 



71 



smaller and more attenuated and eel-like fish than Polypterus ; it 

 has no pelvic fins, and the dorsal fiulets are more isolated, and 

 each spine supports but a single soft ray. The fish lives in shallow- 

 parts of the Senegal and Congo among the interlaced roots of 

 palms. 



Fig. 41. — Larva of Polypterus senegalensis. X 4, showing- the large external 

 gill. (From Bridge, Camb. Nat. Hist., vii, 1904, after Budgett.) 



ASTYLOPTERYGII (Ganoid Fishes without Lobed Fins) . 



In the Astylopterygii the paired fins have not a conspicuous 

 muscular " lobe." The projecting part of the fin consists of skin 

 supported by large bony fin-rays of dermal origin, which articulate 

 at their bases with a row of cartilages or bones, called the pterygia, 

 embedded in the body and connected with the shoulder girdle 

 (see skeleton of pectoral fin of Sturgeon, 209, and of Gar-pike, 217). 

 The pelvic fins are set far behind the pectorals (abdominal 

 position) ; the skull is well protected by dermal bones ; there is no 

 supraoccipital bone. The known range of these fishes is from the 

 Devonian epoch to the present time. In the living representatives, 

 e. g. the Sturgeon, Gar-pike and Bow-fin, the heart has a conus 

 arteriosus provided with two or more rows of valves ; there is a 

 spiral valve in the intestine ; abdominal pores are present ; the 

 air-bladder has an open duct ; the testis is connected with the 

 kidney ; and the optic nerves meet below the brain in the form of 

 a chiasma. There are three suborders, the Sturioniformes or 

 Sturgeons, the Lepidosteiformes or Gar-pikes, and the Amiiformes 

 or Bow-fins. 



