﻿132 
  

  

  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TEIMERELLID^. 
  

  

  transmedial, 
  crossing 
  in 
  a 
  backward 
  direction 
  from 
  the 
  middle 
  of 
  the 
  

   sides 
  of 
  the 
  posterior 
  half 
  of 
  the 
  brachial 
  valve 
  to 
  the 
  reverse 
  sides 
  

   of 
  the 
  pedicle-valve 
  ; 
  the 
  remaining 
  three 
  pairs 
  (laterals) 
  pass 
  from 
  

  

  Fig. 
  1. 
  — 
  Lingula 
  anatina, 
  to 
  illustrate 
  the 
  Scars 
  in 
  Trimerella. 
  

  

  Brachial 
  valve. 
  

  

  Pedicle-valve. 
  

  

  cj. 
  Umbonal 
  muscle, 
  h. 
  Central 
  muscles, 
  i. 
  Transmedial 
  muscles 
  : 
  b. 
  Parietal 
  

  

  band, 
  j, 
  k, 
  I. 
  Lateral 
  muscles 
  (/, 
  anteriors; 
  k, 
  middles; 
  I, 
  outsiders). 
  

  

  A. 
  Splanchnoccele. 
  B. 
  Pleurocceles. 
  C. 
  Brachioccele. 
  

  

  the 
  sidesof 
  the 
  same 
  half 
  of 
  both 
  valves 
  to 
  points 
  farther 
  forward 
  and 
  

   adjacent 
  to 
  the 
  median 
  line 
  of 
  the 
  shell, 
  but 
  without 
  crossing 
  it. 
  

  

  .Reverting 
  to 
  the 
  Trimerellids, 
  we 
  shall 
  make 
  one 
  or 
  two 
  sugges- 
  

   tions 
  respecting 
  the 
  subcardinal 
  scars 
  (w, 
  w). 
  First, 
  they 
  may 
  have 
  

   belonged 
  to 
  a 
  muscle 
  corresponding 
  with 
  the 
  umbonal 
  one 
  of 
  Lingula. 
  

   If, 
  as 
  appears 
  probable, 
  the 
  single 
  umbonal 
  muscle, 
  just 
  referred 
  to, 
  

   is 
  the 
  homologue 
  of 
  the 
  two 
  posterior 
  adductors 
  of 
  Discina, 
  there 
  is 
  

   no 
  reason 
  against 
  assuming 
  that 
  the 
  presumed 
  corresponding 
  muscle 
  

   of 
  the 
  Trimerellids 
  has 
  been 
  simple 
  in 
  certain 
  genera 
  (PI. 
  XII. 
  

   fig. 
  1, 
  w), 
  and 
  compound 
  or 
  double 
  in 
  others 
  (figs. 
  3 
  & 
  5, 
  w)— 
  or 
  

   divided 
  at 
  its 
  attachment 
  in 
  one 
  valve, 
  and 
  undivided 
  in 
  the 
  other. 
  

   Second, 
  they 
  may 
  be 
  the 
  same 
  as 
  the 
  part 
  in 
  the 
  brachial 
  valve 
  we 
  

   have 
  called 
  the 
  cardinal 
  scar 
  (v, 
  fig. 
  2)— 
  a 
  view, 
  however, 
  which 
  re- 
  

  

  