446 
ACTINOPTER YGTI. 
Suborder IV. ISOSPONDYLI. 
Notochord varying in persistence, the vertebral centra usually 
complete, but none coalesced; tail homocercal, but haemal supports 
not much expanded or fused. Symplectic bone present; mandible 
simple, each ramus consisting only of two elements (dentary and 
articulo-angular), with rare rudiments of a splenial on the inner 
side. Pectoral arch suspended from the cranium ; a precoracoid arch 
present, infraclavicular plates wanting; pectoral fin with not more 
than four or five basals. Pelvic fins abdominal. Scales ganoid 
only in the less specialized families. In the living forms—air- 
bladder connected with the oesophagus in the adult, optic nerves 
decussating, and intestine either wanting spiral valve or with an 
incomplete representative of it. 
Synopsis of Families (contained in Part III.). 
I. Margin of upper jaw formed by maxilla and 
premaxilla; parietal hones in contact 
mesiallv. 
Vertebral centra not more than rings; no 
fused or expanded hypurals ; no inter¬ 
muscular bones ; fins fringed with fulcra; 
scales rhombic and ganoid. 
Vertebral centra complete or with minute 
perforation; no fused or expanded hy¬ 
purals ; intermuscular bones rare or 
absent; fins fringed with fulcra; scales 
cycloidal ... 
Vertebral centra nearly complete, but with 
perforation; no fused or expanded hyp¬ 
urals ; intermuscular bones well-devel¬ 
oped ; no fulcra on fins ; scales cycloidal, 
but ganoid . 
Pholidophorid^ 
(p. 446). 
OLIGOPLEURIDiE 
(p. 490). 
LiEPTOLEPIDiE (p. 500). 
(To be continued in Part IV.) 
Family PHOLIDOPHORIMh 
Trunk elegantly fusiform. Head with delicate membrane-bones, 
the suborbital and circumorbital plates completely covering the 
cheek, all enamelled ; snout not produced ; mandibular suspensorium 
nearly vertical or inclined forwards, and gape of mouth wide ; 
premaxilla very small; maxilla large, loosely attached and with two 
well-developed supramaxillary plates ; teeth small and conical. 
Opercular apparatus complete. Vertebral centra never advanced 
