﻿T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMERELLID-E. 
  145 
  

  

  of 
  the 
  valve 
  ; 
  its 
  vaults 
  of 
  greater 
  or 
  lesser 
  depth 
  : 
  median 
  plate 
  

   extending 
  to 
  within 
  a 
  short 
  distance 
  of 
  the 
  anterior 
  edge 
  of 
  the 
  

   shell, 
  dividing 
  it 
  into 
  two 
  lateral 
  portions 
  : 
  archlet 
  wider 
  than 
  the 
  

   platform, 
  passing 
  forward 
  to 
  the 
  end 
  of 
  the 
  median 
  plate. 
  

  

  The 
  discovery 
  of 
  this 
  remarkable 
  species 
  is 
  due 
  to 
  Mr. 
  Billings, 
  

   who, 
  in 
  January 
  1862, 
  published 
  a 
  short 
  description, 
  with 
  figures, 
  of 
  

   an 
  internal 
  cast. 
  He 
  also 
  at 
  the 
  same 
  time 
  proposed 
  for 
  it 
  a 
  new 
  

   generic 
  appellation, 
  stating 
  that 
  it 
  was 
  allied 
  to 
  Obolus, 
  but 
  differed 
  

   from 
  this 
  genus 
  in 
  the 
  possession 
  of 
  three 
  longitudinal 
  septa 
  in 
  each 
  

   valve 
  *. 
  Some 
  good 
  figures 
  of 
  the 
  interior 
  of 
  the 
  shell, 
  taken 
  from 
  

   gutta-percha 
  squeezes, 
  were 
  subsequently 
  published 
  by 
  Professor 
  

   Hall, 
  in 
  1872. 
  

  

  Billings, 
  when 
  noticing 
  the 
  muscular 
  scars 
  of 
  the 
  present 
  species, 
  

   states 
  that 
  " 
  on 
  each 
  side 
  " 
  of 
  the 
  platform 
  " 
  there 
  appears 
  to 
  be 
  a 
  

   small 
  ovate 
  muscular 
  impression 
  as 
  in 
  Obolus" 
  The 
  specimen 
  which 
  

   displays 
  this 
  impression 
  was 
  kindly 
  placed 
  in 
  our 
  hands 
  by 
  Mr. 
  

   Billings. 
  At 
  first 
  we 
  imagined 
  he 
  had 
  correctly 
  interpreted 
  it 
  ; 
  but 
  

   our 
  subsequent 
  investigations, 
  as 
  stated 
  in 
  another 
  place, 
  have 
  con- 
  

   vinced 
  us 
  that 
  the 
  interpretation 
  is 
  not 
  correct. 
  

  

  The 
  impression 
  on 
  each 
  side 
  of 
  the 
  platform 
  belongs 
  to 
  the 
  crescent, 
  

   which, 
  as 
  already 
  shown, 
  has 
  its 
  parallel 
  in 
  the 
  posterior 
  half 
  of 
  both 
  

   valves 
  of 
  Lingida; 
  therefore, 
  instead 
  of 
  having 
  been 
  produced 
  by 
  

   the 
  postadductors, 
  it 
  is 
  more 
  likely 
  to 
  have 
  been 
  formed 
  by 
  the 
  

   implantation 
  of 
  the 
  post- 
  and 
  post-lateral 
  parietals 
  of 
  the 
  splanch- 
  

   nocoele 
  and 
  other 
  organs 
  characterizing 
  the 
  genus 
  referred 
  to. 
  

   These 
  organs, 
  as 
  elsewhere 
  made 
  known, 
  it 
  is 
  highly 
  probable, 
  pro- 
  

   duced 
  the 
  crown 
  and 
  sides 
  of 
  the 
  crescents 
  ; 
  but 
  the 
  ends 
  of 
  the 
  

   crescents 
  (terminating 
  in 
  a 
  line 
  intersecting 
  the 
  anterior 
  portion 
  of 
  

   the 
  platform) 
  are 
  formed 
  by 
  a 
  scar, 
  or 
  rather 
  scars, 
  which 
  there 
  is 
  

   every 
  reason 
  to 
  believe 
  resulted 
  from 
  the 
  posterior 
  attachment 
  of 
  a 
  

   group 
  of 
  slanting 
  or 
  lateral 
  muscles 
  f. 
  

  

  The 
  ends 
  of 
  the 
  crescents 
  escaped 
  our 
  notice 
  when 
  fig. 
  2 
  b, 
  

   PI. 
  XIII. 
  of 
  the 
  present 
  species 
  was 
  drawn 
  : 
  indeed 
  it 
  was 
  only 
  

   after 
  becoming 
  acquainted 
  with 
  the 
  parts 
  corresponding 
  with 
  them 
  

   in 
  Lingida 
  that 
  they 
  disclosed 
  themselves 
  to 
  us. 
  On 
  the 
  right 
  side 
  of 
  

   the 
  specimen, 
  as 
  represented 
  by 
  the 
  figure 
  just 
  noticed, 
  there 
  is 
  tole- 
  

   rably 
  well 
  seen, 
  as 
  in 
  the 
  annexed 
  woodcut 
  (fig. 
  2), 
  the 
  scar 
  s, 
  which, 
  

   from 
  its 
  relative 
  position, 
  we 
  have 
  no 
  doubt 
  is 
  due, 
  as 
  in 
  Lingula 
  

   anatina, 
  to 
  the 
  posterior 
  attachment 
  of 
  the 
  lateral 
  muscles. 
  

  

  The 
  interior 
  of 
  the 
  umbo 
  in 
  the 
  pedicle-valve 
  looks 
  as 
  if 
  it 
  were 
  to 
  

   a 
  slight 
  extent 
  doubly 
  chambered 
  ; 
  the 
  chambers 
  separated 
  by 
  a 
  

   wide 
  cardinal 
  buttress 
  J. 
  The 
  hinge, 
  on 
  the 
  top 
  of 
  the 
  last 
  part, 
  

  

  * 
  We 
  have 
  shown 
  elsewhere, 
  there 
  exists 
  in 
  reality 
  but 
  one 
  septum 
  — 
  -that 
  is, 
  

   the 
  median 
  plate 
  — 
  the 
  other 
  two 
  forming 
  the 
  sides 
  of 
  the 
  platform 
  : 
  the 
  name 
  

   Trimerella 
  is 
  therefore 
  a 
  misnomer. 
  

  

  t 
  See 
  paper 
  on 
  " 
  lAngula 
  anatina" 
  Annals 
  and 
  Mag. 
  of 
  Nat. 
  Hist. 
  4th 
  

   Series, 
  vol. 
  xii. 
  July 
  1873; 
  also 
  woodcuts 
  in 
  p. 
  132. 
  

  

  \ 
  Two 
  figures 
  of 
  this 
  species, 
  representing 
  apparently 
  young 
  individuals, 
  

   given 
  by 
  Professor 
  Hall 
  (Preliminary 
  Notice, 
  1872, 
  pi. 
  xiii. 
  figs. 
  14, 
  15), 
  show 
  

   the 
  umbonal 
  chambers 
  rather 
  well 
  developed, 
  and 
  separated 
  by 
  a 
  narrow 
  

   cardinal 
  buttress. 
  

  

  