﻿424 ACTINOPTEETGII. 



Trunk deeply fusiform; tail hetero- 



cercal ; principal dentition on 



pterygoid and spleuial bones, 



obtuse Platysomatid^: (p. 527). 



Trunk elongate-fusiform ; tail ab- 



breviate-heterocercal ; teeth 



slender, styliform Catopterid^ (Part III.). 



B. Degenerate Series. (See Part III.) 

 Cranial shield without a median 



azygous series of bones ; 



branchiostegal rays present ; no 



teeth in adult; tail heterocer- 



cal ; squamation rudimentary 



or absent, except on the upper 



caudal lobe Chondbosteid^:. 



Cranial shield without a median 



azygous series of bones ; 



branchiostegal rays present ; 



teeth in adult ; tail diphycer- 



cal ; longitudinal series of 



scutes upon trunk Belonorhynchidje. 



Cranial shield with a median azygous 



series of bones ; no branchio- 

 stegal rays ; no teeth in adult ; 



tail heterocercal ; longitudinal 



series of scutes upon trunk. . . . Acipenserid^e. 

 Cranial shield with a median 



azygous series of bones ; no 



branchiostegal rays ; minute 



teeth in adult ; tail heterocercal; 



squamation rudimentary or 



absent, except on the upper 



caudal lobe Polyodontid^:. 



Family PAL^EONISCID^E. 



Trunk elongate or elongate-fusiform ; tail heterocercal ; scales 

 rhombic (rarely in part cycloidal), ganoid. Head-bones well-deve- 

 loped, ganoid ; no median series of cranial roof-bones ; teeth slender, 

 conical or styliform ; eye far forwards and snout prominent ; man- 

 dibular suspensorium more or less obliquely directed backwards and 

 downwards. A series of broad branchiostegal rays, the most anterior 

 pair especially large, with a small median element. Dorsal fin single 

 and not much extended. 



This is a somewhat comprehensive family, and it is not unlikely 



