﻿500 
  ACTINOPTERYG1I. 
  

  

  15499. 
  Portion 
  of 
  similar 
  but 
  much 
  larger 
  squamation, 
  exhibiting 
  

   the 
  canal 
  of 
  the 
  lateral 
  line 
  penetrating 
  the 
  scales 
  ; 
  Brazil. 
  

   Completely 
  ossified 
  vertebral 
  centra 
  are 
  shown 
  in 
  the 
  

   section. 
  Purchased, 
  1843. 
  

  

  P. 
  7585. 
  Imperfect 
  caudal 
  pedicle 
  and 
  fin, 
  with 
  similar 
  scales 
  ; 
  

   Brazil. 
  The 
  fin-rays, 
  10 
  or 
  perhaps 
  12 
  in 
  number, 
  are 
  

   extremely 
  robust, 
  much 
  divided, 
  expanded, 
  and 
  closely 
  

   divided 
  distally. 
  The 
  largest 
  measures 
  0*11 
  in 
  length, 
  

   and 
  the 
  fin 
  seems 
  to 
  have 
  been 
  little 
  if 
  at 
  all 
  excavated 
  

   at 
  the 
  hinder 
  border. 
  History 
  unknown. 
  

  

  Family 
  LEPTOLEPID^E. 
  

  

  Trunk 
  elegantly 
  fusiform. 
  Head 
  with 
  delicate 
  membrane-bones, 
  

   the 
  suborbital 
  and 
  circumorbital 
  plates 
  almost 
  or 
  completely 
  cover- 
  

   ing 
  the 
  cheek, 
  more 
  or 
  less 
  enamelled 
  ; 
  parietal 
  bones 
  meeting 
  in 
  

   the 
  middle 
  line 
  ; 
  snout 
  not 
  produced 
  ; 
  mandibular 
  suspensorium 
  

   nearly 
  vertical 
  or 
  inclined 
  forwards, 
  but 
  gape 
  of 
  mouth 
  wide 
  ; 
  pre- 
  

   maxilla 
  very 
  small 
  ; 
  maxilla 
  large, 
  loosely 
  attached 
  and 
  with 
  two 
  

   well-developed 
  supramaxillary 
  plates 
  ; 
  teeth 
  small 
  and 
  conical. 
  

   Opercular 
  apparatus 
  complete. 
  Vertebral 
  centra 
  well- 
  ossified, 
  but 
  

   always 
  pierced 
  by 
  the 
  notochord 
  ; 
  ribs 
  delicate 
  ; 
  no 
  fused 
  or 
  ex- 
  

   panded 
  haemal 
  arches 
  at 
  the 
  base 
  of 
  the 
  tail. 
  Intermuscular 
  bones 
  

   present. 
  Fin-fulcra 
  absent 
  ; 
  fin-rays 
  more 
  or 
  less 
  divided 
  and 
  

   articulated 
  distally 
  ; 
  dorsal 
  and 
  anal 
  fins 
  small, 
  the 
  former 
  usually 
  

   short-based, 
  above 
  or 
  behind 
  the 
  pelvic 
  pair. 
  Scales 
  thin, 
  cycloidal 
  

   and 
  deeply 
  imbricating, 
  usually 
  ganoid 
  in 
  their 
  exposed 
  portion 
  ; 
  

   lateral 
  line 
  not 
  observable. 
  

  

  Synopsis 
  of 
  Genera. 
  

  

  I. 
  Dorsal 
  fin 
  in 
  advance 
  of 
  anal 
  fin, 
  which 
  is 
  not 
  

  

  much 
  extended. 
  

   Dentary 
  bone 
  sharply 
  rising 
  into 
  a 
  thickened 
  

  

  obtuse 
  elevation 
  near 
  its 
  anterior 
  end 
  . 
  . 
  Leptolepis 
  (p. 
  501). 
  

   Dentary 
  bone 
  gradually 
  deepening 
  from 
  the 
  

  

  symphysis 
  backwards 
  without 
  any 
  marked 
  

  

  thickening 
  Aethalion 
  (p. 
  518). 
  

  

  II. 
  Dorsal 
  fin 
  opposed 
  to 
  anal 
  fin, 
  which 
  is 
  much 
  

  

  extended. 
  

   Dentary 
  bone 
  as 
  in 
  Aethalion 
  Thrissops 
  (p. 
  521). 
  

  

  