﻿EUGNATHIDJ5. 
  317 
  

  

  arranged 
  in 
  close 
  series 
  ; 
  preoperculum 
  almost 
  or 
  completely 
  covered 
  

   by 
  the 
  cheek-plates; 
  operculum 
  quadrangular, 
  broader 
  above 
  than 
  

   below 
  ; 
  suboperculum 
  large, 
  trapezoidal, 
  deeper 
  behind 
  than 
  in 
  

   front, 
  and 
  without 
  an 
  ascending 
  process 
  at 
  its 
  antero-superior 
  angle 
  ; 
  

   branchiostegal 
  rays 
  few 
  and 
  broad, 
  and 
  a 
  very 
  large 
  gular 
  plate 
  

   present, 
  these 
  being 
  comparatively 
  smooth. 
  [Annular 
  ossifications 
  

   in 
  the 
  sheath 
  of 
  the 
  notochord 
  known 
  only 
  at 
  the 
  base 
  of 
  the 
  tail 
  

   in 
  one 
  specimen.] 
  Fulcra 
  biserial, 
  conspicuous 
  on 
  all 
  the 
  fins 
  

   except 
  the 
  dorsal 
  ; 
  fin-rays 
  more 
  or 
  less 
  ornamented 
  with 
  ridges 
  

   of 
  ganoine. 
  Pectoral 
  much 
  exceeding 
  the 
  pelvic 
  fins 
  in 
  size, 
  but 
  

   the 
  latter 
  well-developed 
  ; 
  dorsal 
  and 
  anal 
  fins 
  triangular 
  in 
  shape, 
  

   the 
  former 
  opposed 
  to 
  the 
  pelvic 
  pair, 
  the 
  latter 
  small 
  and 
  remote 
  ; 
  

   caudal 
  fin 
  deeply 
  forked. 
  Scales 
  thick 
  and 
  deeply 
  overlapping, 
  

   destitute 
  of 
  an 
  inner 
  rib, 
  but 
  those 
  of 
  the 
  flank 
  with 
  a 
  peg-and- 
  

   socket 
  articulation 
  ; 
  the 
  external 
  layer 
  of 
  ganoine 
  marked 
  with 
  

   deep 
  longitudinal 
  grooves 
  ; 
  all 
  the 
  scales 
  much 
  longer 
  than 
  deep, 
  

   but 
  especially 
  elongated 
  in 
  the 
  ventral 
  region 
  ; 
  no 
  enlarged 
  series 
  

   of 
  ridge-scales, 
  but 
  some 
  enlarged 
  on 
  the 
  inner 
  side 
  of 
  the 
  pectoral 
  

   and 
  pelvic 
  fins, 
  three 
  large 
  scales 
  surrounding 
  the 
  anus 
  in 
  advance 
  

   of 
  the 
  anal 
  fin, 
  and 
  some 
  large 
  postclaviculars 
  conspicuous. 
  Lateral 
  

   line 
  obscurely 
  marked, 
  opening 
  on 
  the 
  scales 
  by 
  widely-separated 
  

   vertical 
  slits. 
  

  

  The 
  character 
  of 
  the 
  external 
  ornament 
  renders 
  it 
  difficult 
  to 
  

   observe 
  the 
  sutures 
  between 
  the 
  head-bones 
  in 
  Ptycholepis 
  ; 
  and 
  the 
  

   dense 
  squamation 
  obscures 
  the 
  endoskeleton 
  of 
  the 
  trunk 
  in 
  all 
  

   known 
  specimens. 
  The 
  inner 
  bones 
  of 
  the 
  head 
  and 
  the 
  inner 
  

   dentition 
  also 
  remain 
  unknown. 
  

  

  Ptycholepis 
  bollensis, 
  Agassiz. 
  

  

  1832. 
  Ptycholepis 
  bollensis, 
  L. 
  Agassiz, 
  Neues 
  Jahrb. 
  p. 
  142 
  (name 
  

  

  only). 
  

   1833-44. 
  Ptycholepis 
  bollensis, 
  L. 
  Agassiz, 
  Poiss. 
  Foss. 
  vol. 
  ii. 
  pt. 
  i. 
  p. 
  11, 
  

  

  pt. 
  ii. 
  p. 
  108, 
  pi. 
  lviii. 
  b. 
  

   1849. 
  Ptycholepis 
  bollensis, 
  W. 
  C. 
  Williamson, 
  Phil. 
  Trans. 
  1849, 
  

  

  p. 
  444. 
  

   1852. 
  Ptycholepis 
  bollensis, 
  F. 
  A. 
  Quenstedt, 
  Handb. 
  Petrefakt. 
  p. 
  203, 
  

  

  pi. 
  xv. 
  fig. 
  5. 
  

   1858. 
  Ptycholepis 
  bollensis, 
  F. 
  A. 
  Quenstedt, 
  Der 
  Jura, 
  p. 
  231, 
  pi. 
  xxx. 
  

  

  figs. 
  1-7, 
  pi. 
  xxxi. 
  fig. 
  8. 
  

   1865. 
  Ptycholepis 
  bollensis, 
  G. 
  Cotteau, 
  Bull. 
  Soc. 
  Sci. 
  Yonne, 
  vol. 
  xix. 
  

  

  pt. 
  ii. 
  p. 
  337. 
  

   1875. 
  Ptycholepis 
  barrati, 
  H. 
  E. 
  Sauvage, 
  Bibl. 
  £cole 
  Hautes 
  Etudes, 
  

  

  vol. 
  xiv. 
  no. 
  1, 
  p. 
  8, 
  pi. 
  ii. 
  fig. 
  2. 
  [Distorted 
  fish.] 
  

   1891. 
  Ptycholepis 
  barrati, 
  H. 
  E. 
  Sauvage, 
  Bull. 
  Soc. 
  Sci. 
  Yonne, 
  

  

  vol. 
  xlv. 
  pt. 
  ii. 
  p. 
  33, 
  pi. 
  i. 
  

  

  