﻿418 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [June 
  22, 
  

  

  generally 
  the 
  appearance 
  of 
  being 
  cut 
  sharply 
  across 
  at 
  the 
  point 
  of 
  

   insertion. 
  The 
  spines 
  are, 
  for 
  the 
  most 
  part, 
  deeply 
  grooved 
  with 
  

   intermediate 
  bold 
  ridges. 
  The 
  implanted 
  portion 
  is 
  seldom 
  in 
  a 
  

   sufficient 
  state 
  of 
  preservation 
  to 
  exhibit 
  any 
  markings 
  ; 
  I 
  have, 
  

   however, 
  seen 
  one 
  or 
  two 
  casts 
  showing 
  it 
  distinctly 
  striated, 
  the 
  

   striae 
  being 
  much 
  more 
  numerous 
  and 
  much 
  shallower 
  than 
  in 
  the 
  

   exposed 
  part 
  of 
  the 
  spine. 
  The 
  pectoral 
  spines 
  in 
  all 
  seem 
  to 
  have 
  

   been 
  articulated 
  with 
  the 
  pectoral 
  arches 
  ; 
  in 
  some, 
  as 
  in 
  Climatius, 
  

   these 
  appear 
  to 
  have 
  been 
  completely 
  anchylosed. 
  

  

  The 
  scales 
  also 
  appear 
  to 
  have 
  somewhat 
  of 
  an 
  intermediate 
  cha- 
  

   racter. 
  These 
  in 
  all 
  the 
  Forfarshire 
  genera 
  are 
  small, 
  in 
  some 
  

   very 
  small, 
  and 
  of 
  a 
  rhomboidal 
  form. 
  Their 
  external 
  surface 
  is 
  

   smooth 
  and 
  shining, 
  without 
  the 
  slightest 
  trace 
  of 
  sculpturing. 
  This 
  

   seems 
  to 
  have 
  been 
  the 
  case 
  in 
  all 
  the 
  Devonian 
  Acanthodidce 
  I 
  

   have 
  examined. 
  In 
  most, 
  this 
  surface 
  is 
  much 
  raised 
  towards 
  the 
  

   centre 
  of 
  the 
  scale, 
  so 
  that 
  patches 
  of 
  them, 
  especially 
  in 
  some 
  

   rather 
  imperfectly 
  preserved 
  specimens, 
  have 
  the 
  appearance 
  of 
  sha- 
  

   green. 
  The 
  inner 
  surface 
  in 
  some 
  species, 
  as 
  in 
  Acanthodes 
  Mitchelli, 
  

   is 
  perfectly 
  smooth 
  and 
  quite 
  similar 
  to 
  the 
  exterior 
  ; 
  in 
  others, 
  as 
  in 
  

   Euthacanthus 
  McNicoli, 
  it 
  is 
  sculptured 
  ; 
  and 
  in 
  others, 
  again, 
  as 
  in 
  

   Climatius 
  reticidatus, 
  it 
  is 
  both 
  sculptured 
  and 
  tuberculated. 
  The 
  in- 
  

   ternal 
  structure 
  of 
  the 
  scale 
  is 
  sometimes 
  preserved, 
  but 
  always 
  in- 
  

   distinctly. 
  Considerable 
  misconception 
  as 
  to 
  the 
  true 
  nature 
  of 
  the 
  

   scales 
  of 
  these 
  Fishes 
  has, 
  in 
  my 
  opinion, 
  arisen 
  from 
  sufficient 
  at- 
  

   tention 
  not 
  having 
  been 
  paid 
  to 
  whether 
  the 
  exterior 
  or 
  interior 
  

   surface 
  of 
  the 
  scale 
  is 
  shown 
  in 
  specimens 
  : 
  this 
  is 
  well 
  exemplified 
  

   in 
  the 
  descriptions 
  of 
  Diplacanthus 
  longispinus, 
  a 
  common 
  species, 
  

   the 
  scales 
  of 
  which 
  are 
  always 
  said 
  to 
  be 
  sculptured. 
  In 
  this 
  Fish 
  it 
  

   is 
  generally 
  the 
  inner 
  surface 
  of 
  the 
  scale, 
  or 
  its 
  cast, 
  which 
  is 
  exhi- 
  

   bited, 
  but 
  in 
  some 
  few 
  cases 
  the 
  exterior 
  surface 
  is 
  shown. 
  It 
  is 
  quite 
  

   smooth, 
  and 
  so 
  raised 
  in 
  the 
  centre 
  as 
  to 
  present 
  a 
  mammillated 
  ap- 
  

   pearance. 
  That 
  the 
  sculptured 
  surface 
  is 
  the 
  interior, 
  the 
  two 
  fol- 
  

   lowing 
  reasons 
  will, 
  I 
  think, 
  suffice 
  to 
  prove. 
  First, 
  the 
  sculpture 
  

   in 
  the 
  scales 
  of 
  Diplacanthus 
  longispinus 
  consists 
  of 
  well-marked 
  

   striae 
  extending 
  from 
  the 
  anterior 
  margin 
  of 
  the 
  scale 
  to 
  nearly 
  its 
  

   centre, 
  leaving 
  the 
  posterior 
  half 
  smooth 
  ; 
  in 
  scales 
  sculptured 
  ex- 
  

   ternally 
  the 
  sculpture 
  is 
  most 
  marked 
  on 
  the 
  posterior 
  half. 
  Second, 
  

   in 
  Diplacanthus 
  longispinus 
  there 
  is 
  little 
  overlap, 
  but 
  sufficient 
  to 
  

   show 
  that 
  the 
  smooth 
  portion 
  was 
  overlapped 
  by 
  the 
  striated 
  ; 
  in 
  

   other 
  words, 
  that 
  the 
  overlap 
  was 
  towards 
  the 
  head 
  of 
  the 
  Fish, 
  which 
  

   could 
  only 
  have 
  been 
  from 
  the 
  interior 
  surface 
  being 
  that 
  shown. 
  

   In 
  other 
  genera 
  the 
  same 
  peculiarities 
  are 
  found 
  : 
  it 
  is 
  very 
  marked 
  

   in 
  some 
  of 
  the 
  Forfarshire 
  genera, 
  as 
  will 
  be 
  noticed 
  in 
  describing 
  

   them. 
  I 
  merely 
  instance 
  Diplacanthus 
  longispinus 
  as 
  being 
  well 
  

   known 
  and 
  having 
  comparatively 
  large 
  scales 
  with 
  well-marked 
  striae. 
  

   The 
  object 
  of 
  these 
  sculp 
  turings 
  appears 
  to 
  have 
  been 
  to 
  afford 
  means 
  

   for 
  the 
  firmer 
  adhesion 
  of 
  their 
  scales 
  to 
  the 
  integument 
  covering 
  

   the 
  body 
  of 
  the 
  Fish. 
  

  

  With 
  the 
  exception 
  of 
  Acanthodes 
  Mitchelli, 
  and 
  in 
  a 
  less 
  degree 
  

   Ischnacanthus 
  gracilis, 
  none 
  of 
  the 
  Forfarshire 
  Acanthodians 
  show 
  

  

  