﻿446 
  

  

  ACTINOPTEKYGII. 
  

  

  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 
  bones 
  in 
  contact 
  

   mesially. 
  

  

  Vertebral 
  centra 
  not 
  more 
  than 
  rings 
  ; 
  no 
  

   fused 
  or 
  expanded 
  hypurals 
  ; 
  no 
  inter- 
  

   muscular 
  bones 
  ; 
  fins 
  fringed 
  with 
  fulcra 
  ; 
  

   scales 
  rhombic 
  and 
  ganoid 
  Pholidophorid^i 
  

  

  Vertebral 
  centra 
  complete 
  or 
  with 
  minute 
  (p. 
  446). 
  

  

  perforation; 
  no 
  fused 
  or 
  expanded 
  hy- 
  

   purals; 
  intermuscular 
  bones 
  rare 
  or 
  

   absent 
  ; 
  fins 
  fringed 
  with 
  fulcra 
  ; 
  scales 
  

   cycloidal 
  Oligopleurid^: 
  

  

  Vertebral 
  centra 
  nearly 
  complete, 
  but 
  with 
  (p. 
  490). 
  

  

  perforation 
  ; 
  no 
  fused 
  or 
  expanded 
  hyp- 
  

   urals; 
  intermuscular 
  bones 
  well-devel- 
  

   oped 
  ; 
  no 
  fulcra 
  on 
  fins 
  ; 
  scales 
  cycloidal, 
  

   but 
  ganoid 
  Lbptolepidje 
  (p. 
  500). 
  

  

  (To 
  be 
  continued 
  in 
  Part 
  IV.) 
  

  

  Family 
  PHOLIDOPHORIM]. 
  

  

  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 
  ; 
  teetb 
  small 
  and 
  conical. 
  

   Opercular 
  apparatus 
  complete. 
  Vertebral 
  centra 
  never 
  advanced 
  

  

  