﻿128 
  ACTINOPTERYGII. 
  

  

  Genus 
  DAPEDIUS, 
  Leach 
  {emend. 
  Agassiz). 
  

  

  [Trans. 
  Geol. 
  Soc. 
  (2) 
  vol. 
  i. 
  1822, 
  p. 
  45 
  (Dapedium), 
  and 
  

   Agassiz, 
  Poiss. 
  Eoss. 
  vol. 
  ii. 
  pt. 
  i. 
  1835, 
  p. 
  181.] 
  

  

  Syn. 
  Tetragonolepis, 
  L. 
  Agassiz 
  (non 
  Bronn), 
  Poiss. 
  Foss._vol. 
  ii. 
  pt. 
  i. 
  

  

  1833-35, 
  pp. 
  6, 
  181. 
  

   Amblyurus, 
  L. 
  Agassiz, 
  ibid. 
  1836, 
  p. 
  220. 
  

   JEchmodus, 
  Sir 
  P. 
  Egerton, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  x. 
  1854, 
  

  

  p. 
  367. 
  

   Omalopleurus, 
  0. 
  G. 
  Costa, 
  Ittiol. 
  Foss. 
  Ital. 
  1873, 
  p. 
  59. 
  

  

  Trunk 
  much 
  laterally 
  compressed, 
  cycloidal 
  or 
  very 
  deeply 
  fusi- 
  

   form. 
  Head 
  comparatively 
  small, 
  with 
  well-developed 
  opercular 
  

   bones 
  arranged 
  in 
  an 
  arched 
  series 
  ; 
  operculum 
  deeper 
  than 
  the 
  

   suboperculum 
  ; 
  preoperculum 
  narrow 
  and 
  almost 
  or 
  completely 
  

   covered 
  by 
  the 
  suborbitals, 
  but 
  all 
  the 
  other 
  external 
  bones 
  more 
  

   or 
  less 
  ornamented 
  with 
  tuberculations 
  of 
  ganoine 
  ; 
  a 
  large 
  gular 
  

   plate 
  present. 
  Teeth 
  robust, 
  styliform, 
  with 
  simple, 
  bifid, 
  or 
  mamilli- 
  

   form 
  apex, 
  arranged 
  in 
  clusters 
  within 
  the 
  mouth. 
  Notochord 
  

   persistent; 
  ribs 
  ossified. 
  Pin-fulcra 
  large 
  and 
  uuiserial. 
  Paired 
  

   fins 
  small, 
  and 
  the 
  pectorals 
  situated 
  well 
  upon 
  the 
  flank 
  ; 
  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 
  

   slightly 
  forked. 
  Scales 
  quadrangular, 
  robust, 
  ornamented 
  with 
  

   tubercles 
  dorsally 
  and 
  ventrally, 
  nearly 
  smooth 
  or 
  similarly 
  orna- 
  

   mented 
  on 
  the 
  flanks, 
  and 
  united 
  by 
  a 
  peg-and-socket 
  articulation 
  

   at 
  a 
  slight 
  rib-like 
  thickening 
  anteriorly 
  ; 
  scales 
  of 
  the 
  flank 
  deeper 
  

   than 
  broad, 
  the 
  others 
  nearly 
  equilateral, 
  and 
  the 
  dorsal 
  and 
  ventral 
  

   ridge-series 
  inconspicuous. 
  

  

  The 
  chondrocranium 
  of 
  Dcvpedius 
  is 
  well 
  ossified, 
  and 
  there 
  seems 
  

   to 
  have 
  been 
  a 
  complete, 
  or 
  nearly 
  complete, 
  interorbital 
  septum. 
  

   As 
  seen 
  in 
  side 
  view, 
  the 
  basicranial 
  axis 
  is 
  sharply 
  bent 
  upwards 
  

   in 
  front 
  of 
  the 
  otic 
  region 
  ; 
  and 
  the 
  basioccipital 
  element 
  is 
  deep 
  y 
  

   much 
  excavated 
  behind 
  for 
  the 
  notochord, 
  and 
  longitudinally 
  

   grooved 
  below 
  for 
  the 
  basicranial 
  canal. 
  The 
  divisions 
  between 
  

   the 
  elements 
  of 
  the 
  cranium 
  and 
  the 
  situation 
  of 
  the 
  foramina 
  for 
  

   the 
  nerves 
  have 
  unfortunately 
  not 
  hitherto 
  been 
  distinguished 
  ; 
  but 
  

   it 
  is 
  clear 
  that 
  there 
  was 
  an 
  ossified 
  supraoccipital, 
  with 
  a 
  vertical 
  

   median 
  ridge 
  behind, 
  and 
  there 
  are 
  robust 
  ossifications 
  in 
  the 
  pre- 
  

   frontal 
  and 
  postfrontal 
  regions. 
  The 
  ethmoidal 
  region 
  terminates 
  

   in 
  front 
  in 
  a 
  small 
  blunt 
  process, 
  pierced 
  transversely 
  by 
  a 
  large 
  

   foramen 
  ; 
  it 
  expands 
  on 
  each 
  side, 
  in 
  advance 
  of 
  and 
  below 
  the 
  pre- 
  

   frontal, 
  into 
  a 
  great 
  mass 
  sheathed 
  by 
  the 
  vomer. 
  The 
  olfactory 
  

   nerve 
  evidently 
  passed 
  through 
  a 
  foramen 
  observable 
  between 
  the 
  

  

  