﻿T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMERELLIDS. 
  135 
  

  

  these 
  vaults. 
  Lindstrb'm 
  supposes 
  them 
  to 
  have 
  been 
  hollows 
  in 
  which 
  

   the 
  muscles 
  were 
  implanted*. 
  "We 
  have 
  searched 
  for 
  impressions 
  

   likely 
  to 
  have 
  resulted 
  from 
  such 
  implantation, 
  but 
  without 
  success 
  ; 
  

   and 
  it 
  appears 
  highly 
  improbable 
  that 
  the 
  vaults, 
  which 
  run 
  the 
  

   entire 
  length 
  of 
  the 
  platforms 
  up 
  to 
  the 
  hinge 
  in 
  certain 
  species, 
  

   could 
  have 
  served 
  this 
  purpose 
  f. 
  

  

  We 
  may 
  leave 
  for 
  a 
  short 
  while 
  the 
  consideration 
  of 
  the 
  internal 
  

   parts 
  of 
  the 
  Trimerellids 
  to 
  take 
  a 
  passing 
  notice 
  of 
  the 
  hinge-cha- 
  

   racters. 
  These 
  clearly 
  show 
  that 
  the 
  shells 
  have 
  been 
  furnished 
  

   with 
  a 
  massive 
  pedicle, 
  closely 
  agreeing 
  in 
  its 
  attachments 
  with 
  that 
  

   of 
  Idngula. 
  As 
  in 
  this 
  shell, 
  the 
  proximal 
  extremity 
  of 
  the 
  pedicle 
  

   in 
  the 
  fossil 
  (doubtless 
  in 
  the 
  form 
  of 
  a 
  flatly 
  compressed 
  cylinder 
  — 
  

   that 
  is, 
  with 
  two 
  flattened 
  faces) 
  was 
  evidently 
  attached 
  by 
  one 
  of 
  

   its 
  faces 
  to 
  the 
  entire 
  surface 
  of 
  the 
  deltidium, 
  the 
  imbricated 
  la- 
  

   minse 
  of 
  which 
  are 
  the 
  marks 
  of 
  attachment. 
  The 
  pedicle 
  of 
  Lin- 
  

   gula 
  is 
  further 
  attached 
  by 
  the 
  end 
  of 
  the 
  same 
  face, 
  also 
  by 
  two 
  

   lateral 
  extremities 
  or 
  lobes, 
  the 
  former 
  to 
  a 
  narrow 
  lineated 
  space 
  in 
  

   front 
  of 
  the 
  deltidium, 
  and 
  each 
  of 
  the 
  latter 
  to 
  a 
  point 
  on 
  both 
  sides 
  

   of 
  the 
  narrow 
  space 
  J. 
  It 
  cannot 
  be 
  objected 
  that 
  the 
  deltidial 
  slope 
  

   (b) 
  of 
  the 
  Trimerellids 
  marks 
  the 
  attachment 
  of 
  the 
  end 
  of 
  the 
  

   adhering 
  face 
  of 
  the 
  pedicle 
  ; 
  and 
  we 
  strongly 
  suspect 
  that 
  the 
  del- 
  

   tidial 
  ridges 
  (c) 
  arid 
  cardinal 
  callosities 
  (e) 
  have 
  resulted 
  from 
  the 
  

   attachment 
  of 
  the 
  lateral 
  lobes. 
  In 
  certain 
  of 
  these 
  fossils, 
  especially 
  

   in 
  Trimeretta 
  galtensis, 
  the 
  deltidium 
  displays 
  a 
  deep 
  median 
  groove 
  

   (PI. 
  XVIII. 
  fig. 
  13), 
  called 
  by 
  Hall 
  the 
  " 
  central 
  pedicle-groove," 
  

   a 
  peculiarity 
  we 
  would 
  suggest 
  as 
  being 
  due 
  to 
  the 
  strong 
  attach- 
  

   ment 
  of 
  the 
  middle 
  part 
  of 
  the 
  adhering 
  face 
  of 
  the 
  pedicle, 
  as 
  

   evidence 
  of 
  the 
  kind 
  occasionally 
  occurs 
  in 
  specimens 
  of 
  Lingula 
  

   anatina. 
  It 
  requires 
  to 
  be 
  mentioned 
  that 
  in 
  the 
  latter 
  shell 
  the 
  

   face, 
  end, 
  and 
  lobes 
  spoken 
  of 
  belong 
  to 
  the 
  corneous 
  sheath 
  of 
  the 
  

  

  * 
  Lintlstrom, 
  who 
  speaks 
  of 
  the 
  platform-vaults 
  as 
  " 
  prolonged 
  muscular 
  

   scars," 
  states 
  that 
  the 
  corresponding 
  parts 
  in 
  Lingula 
  are 
  occupied 
  by 
  two 
  im- 
  

   pressions 
  of 
  the 
  adductors. 
  Greol. 
  Mag. 
  vol. 
  v. 
  p. 
  442, 
  1868. 
  

  

  t 
  In 
  a 
  letter 
  received 
  by 
  us 
  from 
  Mr. 
  Whitfield, 
  dated 
  the 
  4th 
  of 
  Dec, 
  1871, 
  

   he 
  states, 
  "In 
  relation 
  to 
  the 
  uses 
  of 
  the 
  cavities 
  beneath 
  the 
  plate 
  [platform], 
  

   they 
  certainly 
  could 
  not 
  have 
  contained 
  any 
  part 
  of 
  the 
  adductor 
  muscles 
  ; 
  but, 
  

   from 
  the 
  large 
  size 
  of 
  these 
  muscles 
  necessary 
  to 
  work 
  such 
  large 
  and, 
  in 
  one 
  

   species 
  [71 
  ohioensis], 
  ponderous 
  shells, 
  the 
  greater 
  part 
  of 
  the 
  surface 
  of 
  this 
  

   part 
  (the 
  cardinal 
  half) 
  of 
  the 
  shell 
  would 
  necessarily 
  be 
  taken 
  up 
  by 
  them, 
  and 
  

   there 
  would 
  be 
  but 
  little 
  space 
  left 
  for 
  the 
  pallial 
  sinuses 
  containing 
  the 
  testes 
  or 
  

   ovaries 
  ; 
  and 
  the 
  plate 
  [platform] 
  is 
  consequently 
  raised 
  to 
  get 
  these 
  large 
  

   muscles 
  out 
  of 
  the 
  way 
  in 
  the 
  centre 
  of 
  the 
  valve, 
  and 
  to 
  let 
  the 
  organs 
  (sexual) 
  

   pass 
  beneath 
  them. 
  This 
  I 
  conceive 
  to 
  be 
  the 
  use 
  of 
  them. 
  I 
  have 
  often 
  thought 
  

   the 
  matter 
  over 
  when 
  explaining 
  these 
  and 
  allied 
  forms. 
  In 
  one 
  form, 
  Pentamerus 
  

   galeatus, 
  many 
  of 
  which 
  I 
  have 
  examined, 
  I 
  know 
  the 
  roughened 
  spaces 
  known 
  

   as 
  ovarian 
  spaces 
  are 
  carried 
  inwards, 
  close 
  to 
  the 
  sides 
  of 
  the 
  thin 
  central 
  septum, 
  

   leaving 
  no 
  space 
  between 
  them 
  such 
  as 
  we 
  see 
  occupying 
  the 
  centre 
  of 
  Orthis 
  

   and 
  allied 
  forms, 
  as 
  well 
  as 
  in 
  most 
  Brachiopoda." 
  

  

  | 
  We 
  have 
  previously 
  noticed 
  the 
  two 
  incised 
  lines 
  in 
  connexion 
  with 
  the 
  

   deltidial 
  ridges 
  : 
  these 
  lines, 
  we 
  believe, 
  are 
  likewise 
  produced 
  by 
  the 
  attach- 
  

   ment 
  of 
  the 
  lateral 
  lobes 
  ; 
  also 
  the 
  corresponding 
  lines 
  occasionally 
  seen 
  on 
  

   the 
  area 
  of 
  certain 
  Spirifers. 
  The 
  transverse 
  striae 
  on 
  the 
  areal 
  borders, 
  as 
  well 
  

   as 
  those 
  on 
  the 
  outside 
  of 
  the 
  hinge 
  in 
  the 
  brachial 
  valve, 
  are 
  evidently 
  due 
  to 
  

   epidermal 
  or 
  external 
  lines 
  of 
  growth, 
  as 
  in 
  Lingula. 
  

  

  