428 



ZOOLOGY. 



The singular spoon-bill, Polyodon folium Lacepede, is five- 

 feet long; it is smooth-skinned and has a snout one-third as 

 long as the body, and spatulate, with thin edges. It has 

 a very wide mouth with minute teeth, 

 and lives on small Crustacea. It abounds 

 in the Mississippi and its larger tribu- 

 taries. 



Order 2. Branchioganoidei. Here be- 

 longs the Polypterus of the Nile and 

 Senegal. In these Ganoids the tail is 

 either protocercal or heterocercal ; tho 

 scales are cycloid or rhomboid. The 

 dorsal fin is long, subdivided into divis- 

 ions, each with a separate ray and spine. 

 Polypterus Uchir Geoffroy (Fig. 393) has 

 a protocercal tail. The young has exter- 

 nal gills (Fig. 394). It inhabits the river 



Fig. 394. External gills of a young Polypterus bichir. 

 br, external gills. 



Nile, P. sencgalus the Senegal. Cola- 

 moichthys differs in having no ventral 

 fins and in its elongated form. It inhabits 

 the rivers of Old Calabar. Allied to 

 these living forms are the Devonian Os- 

 teolepis, Ccelacanthus, and Holoptychius. 

 Order 3. Hyoganoidei. This group is 

 represented by the garpike and Amia or 

 mud-fish of the United States, which 

 is an annectant form connecting the 

 Ganoids with the Teleosts. In these 

 fishes the spinal column is bony, the 

 tail partially heterocercal. 



In Lepidosteus (Fig. 395, L. osseus Agassiz) the body is 

 long, the jaws long and armed with sharp teeth, the vertebrae 

 are opisthocoalous, and the scales are large and rhomboidal, 



jlyptei 

 rvier. 



