﻿158 
  ACTrNOPTEEYGII. 
  

  

  caudal 
  fin. 
  Pelvic 
  fins 
  arising 
  much 
  nearer 
  to 
  the 
  anal 
  than 
  to 
  the 
  

   pectorals 
  ; 
  the 
  dorsal 
  fin, 
  with 
  about 
  24 
  rays, 
  arising 
  considerably 
  

   in 
  advance 
  of 
  the 
  middle 
  point 
  of 
  the 
  back 
  and 
  extending 
  nearly 
  to 
  

   the 
  base 
  of 
  the 
  caudal 
  fin 
  ; 
  the 
  anal 
  fin, 
  with 
  17 
  rays, 
  opposed 
  to 
  

   the 
  hinder 
  two-thirds 
  of 
  the 
  dorsal, 
  and 
  the 
  length 
  of 
  its 
  foremost 
  

   ray 
  equalling 
  nearly 
  half 
  of 
  the 
  maximum 
  depth 
  of 
  the 
  trunk. 
  The 
  

   thickened 
  abdominal 
  squamation 
  terminating 
  abruptly 
  at 
  a 
  line 
  

   joining 
  the 
  origin 
  of 
  the 
  dorsal 
  and 
  anal 
  fins. 
  

  

  Form. 
  Sf 
  Loc. 
  Upper 
  Hawkesbury-Wianamatta 
  Series 
  : 
  Talbralgar, 
  

   New 
  South 
  Wales. 
  

  

  Not 
  represented 
  in 
  the 
  Collection. 
  

  

  Genus 
  TETRAGONOLEPIS, 
  Bronn. 
  

  

  [Neues 
  ahrb. 
  1830, 
  p. 
  30.] 
  

  

  Syn. 
  Pleurolepis, 
  F. 
  A. 
  Quenstedt, 
  Handb. 
  Petrefakt. 
  1852, 
  p. 
  214. 
  

  

  Homoeolepis, 
  A. 
  Wagner, 
  Gelehrte 
  Anzeig. 
  k. 
  bay. 
  Akad. 
  Wiss. 
  

   18G0, 
  p. 
  92. 
  

  

  Trunk 
  much 
  laterally 
  compressed, 
  cycloidal 
  or 
  very 
  deeply 
  

   fusiform, 
  and 
  the 
  abdominal 
  region 
  relatively 
  large, 
  protuberant 
  

   ventrally. 
  Head 
  comparatively 
  small, 
  with 
  well-developed 
  oper- 
  

   cular 
  bones 
  arranged 
  in 
  an 
  arched 
  series 
  ; 
  preoperculum 
  narrow 
  ; 
  

   the 
  external 
  bones 
  in 
  part 
  ornamented 
  with 
  superficial 
  tubercula- 
  

   tions 
  of 
  ganoine. 
  Marginal 
  teeth 
  styliform, 
  in 
  close 
  regular 
  series. 
  

   Notochord 
  persistent, 
  apparently 
  with 
  pleurocentra 
  and 
  hypocentra 
  ; 
  

   ribs 
  short 
  but 
  ossified 
  ; 
  neural 
  spines 
  fused 
  with 
  their 
  supporting 
  

   arches 
  throughout, 
  and 
  both 
  neurals 
  and 
  hsemals 
  in 
  caudal 
  region 
  

   with 
  laminar 
  expansion 
  on 
  anterior 
  border. 
  Pins 
  consisting 
  of 
  

   distally 
  bifurcating 
  rays 
  ; 
  paired 
  fins 
  small, 
  the 
  pectorals 
  situated 
  

   at 
  about 
  the 
  middle 
  of 
  the 
  flank, 
  the 
  pelvic 
  fins 
  remote 
  ; 
  dorsal 
  

   fin 
  much 
  elongated, 
  arising 
  about 
  the 
  middle 
  of 
  the 
  back, 
  and 
  

   anal 
  fin 
  shorter, 
  opposed 
  to 
  the 
  hinder 
  half 
  of 
  the 
  dorsal 
  ; 
  caudal 
  

   fin 
  only 
  slightly, 
  if 
  at 
  all, 
  forked. 
  Scales 
  quadrangular, 
  very 
  deep 
  

   on 
  the 
  flank, 
  smooth, 
  rugose, 
  or 
  tuberculated, 
  and 
  the 
  anterior 
  

   border 
  strengthened 
  by 
  a 
  robust 
  inner 
  rib, 
  which 
  forms 
  the 
  peg- 
  

   and-socket 
  articulation 
  ; 
  caudal 
  scales 
  much 
  thinner 
  than 
  those 
  of 
  

   the 
  abdominal 
  region 
  ; 
  ventral 
  ridge-scales 
  conspicuous, 
  serrated. 
  

  

  Tetragonolepis 
  semicincta, 
  Bronn. 
  

  

  [Plate 
  III. 
  fig. 
  1.] 
  

  

  1830. 
  Tetragonolepis 
  semicinctus, 
  H. 
  G. 
  Bronn, 
  Neues 
  Jahrb. 
  p. 
  30, 
  

  

  pi. 
  i. 
  fig. 
  2. 
  

   1832. 
  Tetragonolepis 
  semicinctus, 
  L. 
  Agassiz, 
  Neues 
  Jahrb. 
  p. 
  147. 
  

  

  