﻿ASPIDORHYNCHIDiE. 
  415 
  

  

  Suborder 
  III. 
  AETHEOSPONDYLL 
  

  

  Notochord 
  varying 
  in 
  persistence, 
  but 
  pleurocentra 
  and 
  hypo- 
  

   centra 
  usually 
  fused, 
  never 
  forming 
  alternating 
  discs 
  or 
  rings 
  ; 
  tail 
  

   abbreviate-heteroeercal 
  or 
  homocercal. 
  Mandible 
  complex, 
  with 
  

   well-developed 
  splenial 
  rising 
  into 
  a 
  coronoid 
  process, 
  which 
  is 
  

   completed 
  by 
  a 
  distinct 
  coronoid 
  bone. 
  Infraclavicular 
  plates 
  

   wanting 
  in 
  the 
  pectoral 
  arch 
  ; 
  pectoral 
  fin 
  with 
  more 
  than 
  five 
  

   basal 
  s. 
  Scales 
  ganoid. 
  In 
  the 
  living 
  forms 
  — 
  air-bladder 
  connected 
  

   with 
  the 
  oesophagus 
  in 
  the 
  adult, 
  optic 
  nerves 
  not 
  decussating, 
  but 
  

   forming 
  a 
  chiasma, 
  and 
  intestine 
  with 
  remnants 
  of 
  a 
  spiral 
  valve. 
  

  

  Synopsis 
  of 
  Families. 
  

  

  A 
  distinct 
  presymphysial 
  bone 
  in 
  man- 
  . 
  

  

  dible 
  ; 
  vertebral 
  centra 
  annular 
  or 
  

  

  amphicoelous 
  ; 
  fin-fulcra 
  minute 
  or 
  

  

  absent 
  Aspidorhynchid^ 
  (p. 
  415). 
  

  

  No 
  presymphysial 
  bone 
  ; 
  vertebral 
  centra 
  

  

  opisthocoelous 
  ; 
  fin-fulcra 
  large 
  .... 
  Lepidosteid^ 
  (p. 
  440). 
  

  

  Family 
  ASPIDORHYNCHID^. 
  

  

  Head 
  and 
  trunk 
  much 
  elongated, 
  the 
  snout 
  produced, 
  and 
  the 
  

   abdominal 
  much 
  longer 
  than 
  the 
  caudal 
  region 
  ; 
  tail 
  homocercal. 
  

   Cranial 
  and 
  facial 
  bones 
  robust 
  and 
  opercular 
  apparatus 
  complete, 
  

   all 
  more 
  or 
  less 
  ganoid 
  ; 
  mandibular 
  suspensorium 
  vertical 
  or 
  

   inclined 
  forwards, 
  but 
  gape 
  of 
  mouth 
  wide 
  ; 
  a 
  distinct 
  azygous 
  pre- 
  

   symphysial 
  bone 
  present 
  in 
  mandible 
  ; 
  marginal 
  teeth 
  slender, 
  

   conical. 
  Branchiostegal 
  rays 
  numerous. 
  Vertebral 
  centra 
  annular 
  

   or 
  amphicoelous. 
  Fins 
  small, 
  with 
  broad 
  flattened 
  rays, 
  branched 
  

   and 
  articulated 
  distally 
  ; 
  fulcra 
  minute 
  or 
  absent. 
  Scales 
  rhombic, 
  

   much 
  deepened 
  on 
  the 
  flank. 
  

  

  Synopsis 
  of 
  Genera. 
  

  

  Rostrum 
  much 
  produced 
  in 
  advance 
  of 
  man- 
  

   dibular 
  symphysis 
  ; 
  an 
  intercalary 
  cheek- 
  

   plate 
  between 
  the 
  suborbitals 
  and 
  pre- 
  

   operculum 
  ; 
  foremost 
  scales 
  of 
  lateral 
  line 
  

   not 
  deeper 
  than 
  those 
  immediately 
  beneath 
  Aspidorhynchus 
  (p. 
  416) 
  , 
  

  

  Rostrum 
  scarcely 
  if 
  at 
  all 
  produced 
  in 
  advance 
  

   of 
  mandibular 
  symphysis; 
  suborbitals 
  in 
  

   contact 
  with 
  preoperculum 
  ; 
  all 
  scales 
  of 
  

   lateral 
  line 
  deeper 
  than 
  those 
  immediately 
  

   beneath 
  „ 
  Belonostomus 
  (p. 
  428). 
  

  

  