FISHES. 213 



ff Scales ganoid, diamond-shaped, enamelled plates; snout 

 lengthened, depressed. . . Rhomboganoidei, DD. 



** Skeleton chiefly cartilaginous ; body naked or with 3 to 5 rows 

 of bony bucklers ; vertical fins with fulcra. (Chondrogan- 



OIDEI.) 



X Mouth terminal, broad ; lower jaw, maxillaries and imlate 

 with many minute, deciduous teeth. Selachostomi, EE. 



Xt Mouth narrow, inferior, toothless. . Chondrostei, FF. 



CC. FAMILIES OF CYCLOGANOIDEI. 



* A broad bony plate between branches of lower jaw; vertical 



fins without fulcra; dorsal fin very long of more than 40 

 rays ; body stout Amiid^, 112. 



DD. FAMILIES OF RHOMBOGANOIDEI. 



^Vertical fins with fulcra ; dorsal short, far back, of less than 12 

 rays ; body elongated. . . . Lepidosteid^, 113. 



EE. FAMILIES OF SELACHOSTOMI. 



* Skin naked ; snout produced into a flat blade ; opercle with a 



long flap POLYODONTID^, 114. 



FF. FAMILIES OF CHONDROSTEI. 



* Body with 5 rows of bony shields (rarely deciduous) ; snout 



produced; four barbels in front of mouth. 



Acipenserid^, 115. 



