428 ZOOLOGY. 
The singular spoon-bill, Polyodon folium Lacepéde, 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. Branchioganoidet.—Here be- 
longs the Polypterus of the Nile and 
Senegal. In these Ganoids the tail is 
either protocercal or heterocercal ; the 
scales are cycloid or rhomboid. The 
dorsal fin is long, subdivided into divis- 
ions, each with a separate ray and spine. 
Polypterus bichir Geoffroy (Fig. 393) has 
a protocercal tail. The young has exter- 
nal gills (Fig. 394). It inhabits the river 
Fig. 394. iene gills of a5 i ung Polypterus bichir. 
br, external gills. 
Nile, P. senegalus the Senegal. Cala- 
motchthys 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, Celacanthus, and Holoptychius. 
Order 3. Hyoganoidei.—This group is 
represented by the garpike and Ama or 
mud-fish of the United States, which 
is an annectant form connecting the 
; Ganoids with the Teleosts. In these 
ae ee Polypte ™* 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 opisthoccelous, and the scales are large and rhomboidal, 
