﻿pycnodontid^:. 
  199 
  

  

  Genus 
  MESODON, 
  Wagner 
  \ 
  

   [Abh. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  math.-phys. 
  CI. 
  vol. 
  vi. 
  1851, 
  p. 
  56.] 
  

   Syn. 
  (?) 
  Typodus, 
  F. 
  A. 
  Quenstedt, 
  Der 
  Jura, 
  1858, 
  p. 
  781. 
  

  

  Trunk 
  discoidal, 
  not 
  produced 
  at 
  the 
  caudal 
  pedicle. 
  Head 
  and 
  

   opercular 
  bones 
  externally 
  ornamented 
  with 
  granulations 
  ; 
  cleft 
  of 
  

   mouth 
  very 
  oblique 
  ; 
  teeth 
  smooth, 
  or 
  with 
  feeble 
  indentation 
  and 
  

   rugse; 
  vomerine 
  teeth 
  arranged 
  in 
  five 
  longitudinal 
  series, 
  the 
  

   lateral 
  pairs 
  being 
  often 
  irregular 
  ; 
  splenial 
  dentition 
  comprising 
  

   one 
  principal 
  series 
  of 
  teeth 
  with 
  three 
  or 
  more 
  outer 
  series 
  and 
  

   one 
  or 
  two 
  inner 
  series, 
  usually 
  irregularly 
  arranged. 
  Neural 
  and 
  

   haemal 
  arches 
  of 
  axial 
  skeleton 
  not 
  sufficiently 
  expanded 
  to 
  meet 
  

   round 
  the 
  notochord. 
  Fin-rays 
  robust, 
  closely 
  articulated, 
  and 
  

   much 
  divided 
  distally. 
  Pelvic 
  fins 
  present 
  ; 
  dorsal 
  and 
  anal 
  fins 
  

   deep 
  throughout 
  their 
  extent, 
  the 
  former 
  occupying 
  the 
  hinder 
  half 
  

   of 
  the 
  back, 
  and 
  the 
  latter 
  somewhat 
  shorter; 
  caudal 
  fin 
  fan- 
  

   shaped, 
  having 
  a 
  convex 
  hinder 
  margin, 
  and 
  arising 
  immediately 
  

   between 
  the 
  posterior 
  extremities 
  of 
  the 
  dorsal 
  and 
  anal 
  fins. 
  

   Scales 
  robust, 
  ornamented 
  with 
  granulations, 
  and 
  occupying 
  only 
  

   the 
  anterior 
  half 
  of 
  the 
  trunk. 
  

  

  Of 
  this 
  genus 
  many 
  species 
  are 
  known 
  only 
  by 
  the 
  dentition, 
  and 
  

   in 
  that 
  case 
  they 
  cannot 
  be 
  satisfactorily 
  defined. 
  The 
  form 
  of 
  the 
  

   teeth 
  is 
  especially 
  variable, 
  but 
  the 
  number 
  and 
  relative 
  proportions 
  

   of 
  the 
  several 
  series 
  appear 
  to 
  be 
  sufficiently 
  constant 
  for 
  noting 
  in 
  

   provisional 
  definitions. 
  

  

  Mesodon 
  macropterus 
  (Agassiz). 
  

   [Plate 
  XVI. 
  fig. 
  1.] 
  

  

  1834-44. 
  Gyrodus 
  macropterus, 
  L. 
  Agassiz, 
  Poiss. 
  Foss., 
  Feuill. 
  p. 
  18, 
  

  

  and 
  vol. 
  ii. 
  pt. 
  ii. 
  p. 
  301. 
  

   1851. 
  Mesodon 
  macropterus, 
  A. 
  Wagner, 
  Abh. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  

  

  math.-phys. 
  CI. 
  vol. 
  vi. 
  pp. 
  49, 
  56, 
  pi. 
  iv. 
  fig. 
  2. 
  

   1856. 
  Mesodon 
  macropterus, 
  J. 
  J. 
  Heckel, 
  Denkschr. 
  k. 
  Akad. 
  Wiss., 
  

  

  math.-naturw. 
  CI. 
  vol. 
  xi. 
  p. 
  202. 
  

   1862. 
  Mesodon 
  macropterus, 
  A. 
  Wagner, 
  Abh. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  

  

  math.-phys. 
  CI. 
  vol. 
  ix. 
  p. 
  349. 
  

   1887. 
  Mesodon 
  macropterus, 
  K. 
  A. 
  von 
  Zittel, 
  Handb. 
  Palseont. 
  vol. 
  iii. 
  

  

  p. 
  247, 
  fig. 
  261. 
  

  

  Type. 
  Nearly 
  complete 
  fish 
  ; 
  Palseontological 
  Museum, 
  Munich. 
  

   The 
  type 
  species, 
  attaining 
  a 
  length 
  of 
  about 
  0*16. 
  Maximum 
  

  

  1 
  This 
  name 
  having 
  gained 
  universal 
  acceptance, 
  we 
  adopt 
  it, 
  notwith- 
  

   standing 
  its 
  preoccupation 
  among 
  Mollusca 
  by 
  Mesodon, 
  Kafinesque, 
  1819. 
  

  

  