424 
ACTINOPTERYGII. 
Trunk deeply fusiform; tail hetero- 
cercal; principal dentition on 
pterygoid and splenial bones, 
obtuse . 
Trunk elongate-fusiform; tail ab- 
breviate-beterocercal; teeth 
slender, styliform. 
JE>. 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 . 
Cranial shield without a median 
azygous series of bones; 
branchiostegal rays present; 
teeth in adult; tail diphycer- 
cal; longitudinal series of 
scutes upon trunk . 
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.... 
Cranial shield w T ith 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. 
Platysomatid.e (p. 527). 
Catopterid.e (Part III.). 
Chondrosteidje. 
BeLONORHYNCHID^E. 
Acipenserid^e. 
P OLYODONTIDJE. 
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 
