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.) 



\ Mouth terminal, broad; lower jaw, maxillaries and palate 



with many minute, deciduous teeth. SELACHOSTOMI, EE. 



$ 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^E, 112. 



DD. FAMILIES OF RHOMBOGANOIDEI. 



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



rays ; body elongated. . . . LEPIDOSTEIELE, 113. 



EE. FAMILIES OF SELACHOSTOMI. 



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



long flap POLYODONTID^E, 114. 



FF. FAMILIES OF CHONDROSTEI. 



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



produced ; four barbels in front of mouth. 



ACIPENSERID., 115. 



