﻿354 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Apr. 
  27, 
  

  

  longest. 
  The 
  structure 
  of 
  the 
  rays 
  resembles 
  that 
  of 
  the 
  last-men- 
  

   tioned 
  fins 
  : 
  the 
  first 
  segment 
  is 
  of 
  considerable 
  length, 
  being 
  fully 
  

   four 
  times 
  as 
  long 
  as 
  those 
  that 
  succeed 
  it 
  ; 
  the 
  succeeding 
  segments 
  

   are 
  slightly 
  shorter 
  than 
  the 
  equivalent 
  segments 
  in 
  the 
  anal 
  and 
  

   dorsal, 
  so 
  as 
  to 
  be 
  wider 
  than 
  long. 
  They 
  appear 
  to 
  bifurcate 
  

   rarely 
  ; 
  and 
  they 
  are 
  covered 
  with 
  longitudinal 
  scales, 
  like 
  those 
  of 
  

   the 
  fins 
  just 
  mentioned. 
  Each 
  lobe 
  is 
  protected 
  along 
  its 
  dorsal 
  and 
  

   ventral 
  borders 
  with 
  comparatively 
  large 
  fulcral 
  scales. 
  The 
  rays 
  of 
  

   the 
  caudal, 
  at 
  least 
  those 
  of 
  the 
  central 
  and 
  ventral 
  portions 
  of 
  it, 
  

   are 
  affixed 
  to 
  long 
  interspinous 
  bones, 
  two 
  rays 
  being 
  attached 
  to 
  

   each. 
  The 
  rays 
  of 
  the 
  anal 
  and 
  dorsal 
  fins 
  are 
  also 
  attached 
  to 
  

   interspinous 
  bones, 
  there 
  being 
  in 
  these 
  instances, 
  however, 
  an 
  

   ossicle 
  to 
  support 
  each 
  ray. 
  

  

  In 
  well-preserved 
  examples 
  the 
  head 
  is 
  seen 
  to 
  be 
  bluntly 
  cone- 
  

   shaped. 
  The 
  gape 
  is 
  comparatively 
  small, 
  and 
  the 
  orbit 
  is 
  large 
  and 
  

   oval. 
  The 
  opercular 
  bones, 
  which 
  form 
  the 
  great 
  bulk 
  of 
  the 
  head, 
  

   have 
  a 
  semicircular 
  edge 
  behind, 
  and 
  a 
  surface 
  with 
  rugulose 
  orna- 
  

   mentation. 
  Below 
  and 
  behind 
  the 
  inferior 
  maxillary 
  are 
  generally 
  

   seen 
  the 
  branchiostegal 
  rays, 
  of 
  which 
  there 
  appear 
  to 
  be 
  nine. 
  

  

  The 
  scales 
  are 
  large, 
  comparatively 
  thick, 
  rhomboidal 
  (variously 
  

   modified), 
  smooth 
  to 
  the 
  eye, 
  but 
  finely 
  shagreened 
  when 
  magnified, 
  

   and 
  with 
  plain 
  margins. 
  The 
  dorso 
  -ventral 
  series 
  are 
  arranged 
  in 
  

   sloping 
  curves 
  ; 
  there 
  are 
  36 
  such 
  series 
  along 
  each 
  flank, 
  and 
  14 
  or 
  

   15 
  scales 
  in 
  each 
  series 
  in 
  the 
  thoracic 
  region. 
  The 
  lateral 
  line 
  is 
  

   marked 
  by 
  a 
  longitudinal 
  series 
  of 
  notched 
  scales, 
  somewhat 
  above 
  

   the 
  centre 
  of 
  the 
  body; 
  these 
  scales 
  are 
  wider 
  than 
  any 
  of 
  the 
  

   others 
  on 
  the 
  flank; 
  the 
  scales 
  above 
  and 
  below 
  the 
  lateral 
  line 
  

   decrease 
  in 
  size 
  gradually, 
  as 
  they 
  do 
  also 
  from 
  the 
  anterior 
  portion 
  

   of 
  the 
  body 
  backward. 
  Though 
  the 
  scales 
  have 
  been 
  described 
  as 
  

   smooth 
  to 
  the 
  eye, 
  it 
  should 
  be 
  mentioned 
  that 
  they 
  are 
  all 
  marked, 
  

   just 
  within 
  their 
  exposed 
  margins, 
  with 
  two 
  or 
  more 
  lines 
  of 
  incre- 
  

   ment 
  of 
  great 
  regularity. 
  The 
  overlap 
  of 
  the 
  scales 
  is 
  considerable 
  ; 
  

   their 
  articulation 
  is 
  assisted 
  also, 
  as 
  in 
  other 
  Palceonisci, 
  (fee, 
  by 
  

   teeth 
  that 
  project 
  from 
  the 
  dorsal 
  margin, 
  and 
  fit 
  into 
  sockets 
  on 
  

   the 
  reverse 
  of 
  the 
  ventral 
  portion 
  of 
  the 
  scales. 
  In 
  advance 
  of 
  each 
  

   lobe 
  of 
  the 
  caudal 
  fin, 
  and 
  of 
  the 
  anal 
  and 
  dorsal, 
  are 
  placed 
  four 
  or 
  

   five 
  large 
  scales, 
  which 
  are 
  altogether 
  different 
  in 
  form 
  from 
  the 
  

   scales 
  of 
  the 
  flank. 
  They 
  graduate 
  from 
  ovate 
  or 
  bluntly 
  pointed 
  

   scales 
  to 
  such 
  as 
  are 
  lanceolate 
  ; 
  and 
  those 
  of 
  the 
  latter 
  form 
  pass 
  

   by 
  insensible 
  modifications 
  into 
  the 
  fulcral 
  scales 
  or 
  rays 
  of 
  the 
  fin- 
  

   borders. 
  

  

  There 
  is 
  more 
  than 
  one 
  species 
  to 
  which 
  this 
  Palceoniscus 
  has 
  

   some 
  resemblance 
  ; 
  P. 
  Voltzii, 
  P. 
  fultus, 
  P. 
  anc/ustus, 
  and 
  P. 
  Vrati- 
  

   slaviensis, 
  for 
  instance, 
  all 
  appear 
  related, 
  though 
  apparently 
  distinct, 
  

   forms. 
  Perhaps 
  the 
  Fish 
  that 
  this 
  species 
  most 
  nearly 
  resembles 
  is 
  

   Palceoniscus 
  glaphyrus, 
  Ag., 
  of 
  the 
  Marl-slate. 
  It 
  resembles 
  it 
  in 
  

   size, 
  largeness 
  of 
  scales, 
  smallness 
  of 
  gape, 
  size 
  of 
  orbit, 
  and 
  in 
  posi- 
  

   tion 
  and 
  structure 
  of 
  fins 
  ; 
  but 
  it 
  differs 
  from 
  it 
  in 
  having 
  a 
  com- 
  

   paratively 
  larger 
  head 
  — 
  the 
  head 
  of 
  P. 
  glaphyrus 
  being 
  only 
  one-fifth 
  

   of 
  the 
  entire 
  length, 
  whereas 
  that 
  of 
  P. 
  Marians 
  reaches 
  one-third 
  — 
  and 
  

  

  