﻿ETJGNATHID^. 
  291 
  

  

  Eugnathus 
  orthostomus, 
  Agassiz. 
  

   [Plate 
  IV. 
  fig. 
  1 
  ; 
  PI. 
  Y. 
  fig. 
  1.] 
  

  

  1825. 
  Lepidosteus? 
  dentosus, 
  C. 
  Koenig, 
  Icon. 
  Foss. 
  Sect. 
  pi. 
  xii. 
  

  

  fig. 
  140. 
  

   1842-44. 
  Eugnathus 
  orthostomus, 
  L. 
  Agassiz, 
  Poiss. 
  Foss. 
  vol. 
  ii. 
  pt. 
  ii. 
  

  

  p. 
  98, 
  pi. 
  lvii 
  a. 
  

   1839-44. 
  Eugnathus 
  speciosus, 
  L. 
  Agassiz, 
  ibid. 
  p. 
  100, 
  pi. 
  lvii. 
  [Head 
  

  

  and 
  scales 
  ; 
  Oxford 
  Museum.] 
  

   1844. 
  Eugnathus 
  scabriusoulus, 
  L. 
  Agassiz, 
  ibid. 
  p. 
  105 
  (name 
  only). 
  

  

  [Jaws, 
  etc. 
  ; 
  British 
  Museum.] 
  

  

  Type. 
  Nearly 
  complete 
  fish 
  ; 
  British 
  Museum. 
  

  

  The 
  type 
  species, 
  attaining 
  a 
  length 
  of 
  about 
  0*6. 
  Length 
  of 
  

   head 
  with 
  opercular 
  apparatus 
  equalling 
  about 
  one-quarter, 
  and 
  

   maximum 
  depth 
  of 
  trunk 
  about 
  one-fifth 
  of 
  the 
  total 
  length 
  of 
  the 
  

   fish 
  ; 
  minimum 
  width 
  of 
  caudal 
  pedicle 
  equalling 
  half 
  the 
  maximum 
  

   depth 
  of 
  the 
  trunk. 
  Head 
  elongated, 
  the 
  roof 
  of 
  the 
  skull 
  being 
  

   about 
  three 
  times 
  as 
  long 
  as 
  its 
  width 
  at 
  the 
  occiput, 
  and 
  all 
  the 
  

   external 
  bones 
  smooth 
  or 
  with 
  few 
  small 
  tuberculations 
  ; 
  hinder 
  

   two 
  -thirds 
  of 
  maxilla 
  bearing 
  comparatively 
  small 
  and 
  slender 
  

   elongated 
  teeth, 
  with 
  stouter 
  conical 
  teeth 
  in 
  front 
  and 
  on 
  the 
  

   premaxilla 
  ; 
  supram 
  axilla 
  much 
  more 
  than 
  half 
  as 
  long 
  as 
  maxilla 
  ; 
  

   dentary 
  bone 
  with 
  few 
  widely 
  spaced, 
  large, 
  stout 
  teeth 
  ; 
  splenial 
  

   teeth 
  small; 
  operculum 
  almost 
  as 
  broad 
  as 
  deep. 
  Dorsal 
  fin 
  as 
  

   deep 
  as 
  long, 
  with 
  about 
  16 
  rays, 
  arising 
  in 
  advance 
  of 
  the 
  middle 
  

   point 
  of 
  the 
  back 
  ; 
  origin 
  of 
  pelvic 
  fins 
  exactly 
  opposite 
  to 
  that 
  of 
  

   the 
  dorsal, 
  and 
  the 
  relatively 
  small 
  anal 
  fin, 
  with 
  about 
  9 
  rays, 
  

   arising 
  at 
  the 
  posterior 
  termination 
  of 
  the 
  latter. 
  Scales 
  richly 
  

   ornamented 
  in 
  the 
  abdominal 
  region, 
  smooth 
  on 
  the 
  caudal 
  pedicle 
  ; 
  

   a 
  few 
  anterior 
  flank-scales 
  slightly 
  deeper 
  than 
  broad. 
  

  

  Form. 
  Sf 
  Loc. 
  Lower 
  Lias 
  : 
  Dorsetshire. 
  

  

  All 
  the 
  following 
  specimens 
  were 
  obtained 
  from 
  the 
  neighbour- 
  

   hood 
  of 
  Lyme 
  Regis 
  : 
  — 
  

  

  P. 
  465. 
  Type 
  specimen 
  described 
  and 
  figured 
  by 
  Agassiz, 
  loc. 
  cit. 
  

   The 
  small 
  teeth 
  in 
  front 
  of 
  the 
  mandible 
  noted 
  in 
  the 
  

   original 
  description 
  are 
  evidently 
  those 
  of 
  the 
  splenial 
  bone, 
  

   and 
  other 
  specimens 
  prove 
  that 
  the 
  enlargement 
  of 
  the 
  

   teeth 
  does 
  not 
  take 
  place 
  in 
  the 
  middle 
  of 
  that 
  bone, 
  but 
  

   at 
  its 
  anterior 
  extremity. 
  In 
  the 
  crushed 
  ventral 
  region 
  

   there 
  are 
  remains 
  of 
  the 
  squamation 
  of 
  a 
  small 
  fish, 
  

   apparently 
  swallowed. 
  Egerton 
  Coll. 
  

  

  v2 
  

  

  