﻿134 
  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TKIMEKELLIDiE. 
  

  

  projecting 
  or 
  anterior 
  portion 
  of 
  the 
  platform 
  belonging 
  to 
  the 
  

   brachial 
  valve 
  of 
  Monomerella 
  and 
  Binobolus 
  ; 
  which 
  genera, 
  it 
  will 
  

   be 
  seen, 
  have 
  no 
  median 
  plate, 
  or 
  only 
  a 
  rudimentary 
  one. 
  But 
  

   considering 
  that 
  in 
  the 
  brachial 
  valve 
  of 
  Trimerella 
  this 
  part 
  is 
  as 
  

   well 
  developed 
  as 
  the 
  ridge 
  in 
  Lingula, 
  or 
  even 
  more 
  so, 
  we 
  are 
  

   strongly 
  persuaded 
  that 
  it 
  or 
  its 
  posterior 
  end 
  was 
  marked 
  by 
  the 
  

   scars 
  in 
  question. 
  

  

  If 
  the 
  median 
  plate 
  of 
  the 
  brachial 
  valve 
  were 
  not 
  a 
  muscular 
  

   fulcrum 
  of 
  the 
  kind, 
  it 
  would 
  have 
  to 
  be 
  considered 
  merely 
  analo- 
  

   gous 
  to 
  the 
  medio-longitudinal 
  ridge 
  of 
  Lingula, 
  and 
  not 
  its 
  homologue 
  ; 
  

   or, 
  instead 
  of 
  belonging 
  essentially 
  to 
  the 
  splanchnoccele, 
  it 
  must 
  be 
  

   an 
  integral 
  part 
  of 
  the 
  brachiocoele. 
  The 
  latter 
  view, 
  however, 
  has 
  

   nothing 
  in 
  its 
  favour 
  ; 
  on 
  the 
  contrary, 
  in 
  all 
  known 
  living 
  Pallio- 
  

   branchs 
  (and 
  most 
  of 
  them 
  have 
  it) 
  the 
  ridge, 
  when 
  present, 
  lies 
  

   within 
  the 
  splanchnoccele, 
  and 
  serves 
  as 
  a 
  muscular 
  fulcrum. 
  

  

  The 
  corresponding 
  plate 
  in 
  the 
  pedicle-valve 
  of 
  Trimerella 
  may 
  

   have 
  been 
  subordinated 
  in 
  the 
  same 
  way 
  ; 
  but 
  we 
  are 
  more 
  inclined 
  

   to 
  believe 
  that 
  it 
  merely 
  strengthened 
  the 
  platform, 
  as 
  we 
  think 
  was 
  

   also 
  the 
  case 
  with 
  the 
  rudimentary 
  one 
  in 
  the 
  brachial 
  valve 
  of 
  

   Binobolus 
  (fig. 
  6, 
  1). 
  

  

  The 
  aberrant 
  Trimerella 
  Billingsii 
  and 
  T. 
  galtensis 
  do 
  not 
  possess 
  

   the 
  median 
  plate 
  in 
  the 
  brachial 
  valve 
  : 
  in 
  these 
  cases 
  the 
  muscles 
  

   would 
  be 
  attached 
  to 
  the 
  anterior 
  portion 
  of 
  the 
  platform, 
  as 
  in 
  

   Binobolus 
  and 
  Monomerella. 
  

  

  Besides 
  their 
  use 
  as 
  muscular 
  fulcra, 
  it 
  may 
  safely 
  be 
  admitted 
  that 
  

   the 
  platforms, 
  to 
  some 
  extent, 
  supported 
  the 
  viscera. 
  "We 
  are 
  in- 
  

   duced 
  to 
  refer 
  the 
  postmedian 
  scar 
  (p, 
  fig. 
  6) 
  to 
  the 
  ovaries. 
  These 
  

   organs 
  have 
  been 
  allocated 
  by 
  Dall 
  and 
  others 
  to 
  the 
  platform-vaults 
  ; 
  

   but 
  their 
  usual 
  position 
  in 
  living 
  Palliobranchs 
  would 
  require 
  them 
  

   to 
  be 
  lodged 
  in, 
  or 
  connected 
  with, 
  the 
  posterior 
  portion 
  of 
  the 
  

   splanchnoccele. 
  We 
  are 
  consequently 
  more 
  disposed 
  to 
  believe, 
  

   considering 
  their 
  postlateral 
  situation 
  in 
  BJiynclionella* 
  , 
  and 
  in 
  

   other 
  shells 
  of 
  its 
  class, 
  that 
  the 
  ovaries 
  were 
  similarly 
  situated 
  in 
  

   the 
  Trimerellidsf 
  : 
  the 
  large 
  umbonal 
  cavities 
  characteristic 
  of 
  cer- 
  

   tain 
  species, 
  seem 
  well 
  adapted 
  for 
  containing 
  them. 
  

  

  The 
  platform-vaults 
  appear, 
  from 
  their 
  contiguity 
  to 
  the 
  usual 
  

   locale 
  of 
  the 
  liver, 
  to 
  be 
  the 
  most 
  likely 
  receptacles 
  for 
  the 
  divisions 
  

   of 
  this 
  organ 
  J. 
  Another 
  view 
  has 
  been 
  taken 
  respecting 
  the 
  use 
  of 
  

  

  * 
  Hancock, 
  Transactions 
  of 
  the 
  Royal 
  Society, 
  vol. 
  cxlviii. 
  pi. 
  lx. 
  fig. 
  3, 
  1858. 
  

  

  t 
  Certain 
  genera, 
  especially 
  Camaroplwria 
  and 
  Pentamerus, 
  have 
  hollows 
  in 
  

   the 
  umbo 
  of 
  the 
  pedicle-valve, 
  not 
  only 
  corresponding 
  with, 
  but 
  evidently 
  ful- 
  

   filling 
  the 
  same 
  office 
  as, 
  the 
  umbonal 
  chambers 
  of 
  the 
  Trimerellids. 
  Many 
  

   years 
  ago 
  one 
  of 
  the 
  writers, 
  studying 
  Camarophoria 
  multiplicata, 
  expressed 
  his 
  

   belief 
  that 
  the 
  spaces 
  within 
  the 
  " 
  vascular 
  circles 
  " 
  occurring 
  in 
  this 
  species 
  

   " 
  were 
  the 
  seats 
  of 
  reproduction." 
  Monograph 
  Permian 
  Fossils, 
  p. 
  116. 
  

  

  \ 
  In 
  our 
  previously 
  published 
  "Remarks 
  on 
  the 
  genera 
  Trimerella, 
  Bino- 
  

   bolus, 
  and 
  Monomerella" 
  we 
  instanced 
  the 
  excavated 
  scars 
  of 
  Obolus, 
  which 
  have 
  

   an 
  overlapping 
  posterior 
  margin, 
  thereby 
  approaching 
  in 
  appearance 
  to 
  the 
  

   platform-vaults 
  of 
  Trimerella 
  ; 
  but 
  these 
  are 
  undoubtedly 
  due 
  to 
  muscular 
  at- 
  

   tachment. 
  In 
  Leptcena 
  Butertrii 
  the 
  myophore 
  of 
  one 
  of 
  the 
  valves 
  is 
  doubly 
  

   vaulted, 
  possibly 
  for 
  holding 
  portions 
  of 
  the 
  liver 
  and 
  a 
  case 
  homologous 
  with 
  

   the 
  platform-vaults 
  of 
  Trimerella. 
  

  

  