﻿222 
  ACTINOPTEEYGII. 
  

  

  with 
  reticulating 
  rug£e 
  and 
  pittings 
  ; 
  teeth 
  smooth, 
  sometimes 
  

   feebly 
  indented 
  in 
  the 
  lateral 
  series 
  ; 
  vomerine 
  teeth 
  in 
  five 
  longi- 
  

   tudinal 
  series, 
  the 
  inner 
  lateral 
  pairs 
  regularly 
  alternating 
  with 
  the 
  

   widely 
  spaced 
  median 
  teeth 
  ; 
  splenial 
  teeth 
  in 
  four 
  series, 
  the 
  

   innermost 
  being 
  relatively 
  small, 
  and 
  the 
  second 
  the 
  largest 
  or 
  

   principal 
  series. 
  Neural 
  and 
  hsemal 
  arches 
  of 
  axial 
  skeleton 
  of 
  

   trunk 
  not 
  expanding 
  sufficiently 
  to 
  encircle 
  the 
  notochord. 
  Pin- 
  

   rays 
  robust, 
  closely 
  articulated, 
  and 
  much 
  divided 
  distally. 
  Pelvic 
  

   fins 
  present 
  ; 
  dorsal 
  and 
  anal 
  fins 
  very 
  high 
  and 
  acuminate 
  in 
  front, 
  

   rapidly 
  becoming 
  low 
  and 
  fringe-like 
  behind, 
  the 
  former 
  occupying 
  

   at 
  least 
  the 
  hinder 
  half 
  of 
  the 
  back 
  and 
  the 
  latter 
  somewhat 
  shorter, 
  

   arising 
  more 
  posteriorly 
  ; 
  caudal 
  fin 
  forked. 
  Scales 
  ornamented 
  

   with 
  reticulating 
  rugse 
  or 
  pittings, 
  and 
  covering 
  only 
  the 
  anterior 
  

   half 
  of 
  the 
  trunk 
  in 
  advance 
  of 
  the 
  median 
  fins, 
  though 
  some- 
  

   times 
  partly 
  extended 
  over 
  the 
  middle 
  of 
  the 
  flank 
  of 
  the 
  caudal 
  

   region. 
  

  

  Microdon 
  elegans, 
  Agassiz. 
  

  

  1833-44. 
  Microdon 
  elegans, 
  L. 
  Agassiz, 
  Poiss. 
  Poss. 
  vol. 
  ii. 
  pt. 
  i. 
  p. 
  16, 
  

  

  pt. 
  ii. 
  p. 
  205, 
  pi. 
  lxix. 
  b. 
  

   (?) 
  1839. 
  Gyrodus 
  laticauda, 
  G. 
  von 
  Minister, 
  Neues 
  Jahrb. 
  p. 
  679. 
  

   1843. 
  Microdon 
  notabilis, 
  G. 
  von 
  Minister, 
  Beitr. 
  Petrefakt. 
  pt. 
  vi. 
  

  

  p. 
  55, 
  pi. 
  ii. 
  fig. 
  2. 
  [Mandibular 
  dentition 
  ; 
  Pakeontological 
  

  

  Museum, 
  Munich.] 
  

   1851. 
  Pycnodus 
  elegans, 
  A. 
  Wagner, 
  Abh. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  math.- 
  

  

  phys. 
  CI. 
  vol. 
  vi. 
  pp. 
  33, 
  36. 
  

   1851. 
  Pycnodus 
  notabilis, 
  A. 
  Wagner, 
  ibid. 
  vol. 
  vi. 
  pp. 
  37, 
  57, 
  pi. 
  hi. 
  

  

  fig. 
  3. 
  

   1862. 
  Microdon 
  elegans, 
  A. 
  Wagner, 
  ibid. 
  vol. 
  ix. 
  p. 
  343. 
  

   (?) 
  1862. 
  Microdon 
  nanus, 
  A. 
  Wagner, 
  ibid. 
  vol. 
  ix. 
  p. 
  344. 
  [Immature 
  

  

  fish; 
  Palaeontological 
  Museum, 
  Munich.] 
  

   1887. 
  Microdon 
  elegans, 
  K. 
  A. 
  von 
  Zittel, 
  Handb. 
  Pakeont. 
  vol. 
  iii. 
  

  

  p. 
  246, 
  fig. 
  259. 
  

  

  Type. 
  Nearly 
  complete 
  fish 
  ; 
  Palaeontological 
  Museum, 
  Munich. 
  

  

  The 
  type 
  species, 
  attaining 
  a 
  length 
  of 
  about 
  0'3. 
  Maximum 
  

   depth 
  of 
  trunk 
  equalling 
  about 
  four-fifths 
  of 
  the 
  length 
  of 
  the 
  head 
  

   and 
  trunk 
  without 
  caudal 
  fin 
  ; 
  head 
  with 
  opercular 
  apparatus 
  

   occupying 
  slightly 
  more 
  than 
  one-quarter 
  of 
  the 
  total 
  length 
  of 
  the 
  

   fish. 
  Splenial 
  teeth 
  closely 
  arranged 
  ; 
  those 
  of 
  the 
  principal 
  series 
  

   somewhat 
  broader 
  than 
  long 
  and 
  truncated 
  at 
  each 
  end 
  ; 
  innermost 
  

   teeth 
  and 
  those 
  of 
  the 
  inner 
  flanking 
  series 
  about 
  equal 
  in 
  size, 
  very 
  

   small 
  and 
  sometimes 
  longer 
  than 
  broad 
  ; 
  outermost 
  teeth 
  irregularly 
  

   quadrate, 
  longer 
  than 
  broad, 
  about 
  half 
  as 
  large 
  as 
  the 
  principal 
  

  

  