﻿T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMERELLIDJ3. 
  131 
  

  

  under 
  consideration, 
  especially 
  its 
  anterior 
  ; 
  for 
  generally 
  the 
  latter 
  

   portion, 
  and 
  the 
  line 
  forming 
  the 
  crown 
  of 
  the 
  crescent, 
  are 
  so 
  inter- 
  

   blended 
  as 
  to 
  prevent 
  either 
  one 
  or 
  the 
  other 
  being 
  individually 
  de- 
  

   fined 
  : 
  still 
  we 
  occasionally 
  perceive 
  appearances 
  favouring 
  the 
  idea 
  

   that 
  they 
  are 
  distinct. 
  

  

  Besides 
  the 
  foregoing 
  there 
  are 
  some 
  other 
  scars 
  that 
  require 
  

   noticing. 
  In 
  the 
  pedicle 
  valve 
  of 
  certain 
  Trimerellas 
  there 
  is 
  an 
  

   appearance 
  of 
  an 
  impression 
  (fig. 
  1, 
  w) 
  situated 
  below 
  the 
  hinge, 
  and 
  

   on 
  the 
  cardinal 
  buttress 
  : 
  in 
  the 
  Monomerellas 
  two 
  impressions 
  occur 
  

   (fig. 
  3, 
  w) 
  similarly 
  situated, 
  i. 
  e. 
  at 
  the 
  base 
  of 
  the 
  cardinal 
  buttress 
  

   or 
  at 
  the 
  posterior 
  end 
  of 
  the 
  platform 
  (j) 
  : 
  and 
  in 
  Dinobolus 
  David- 
  

   soni 
  there 
  are 
  two 
  distinct 
  marks 
  (inadvertently 
  omitted 
  in 
  fig. 
  5, 
  w) 
  

   below 
  or 
  on 
  the 
  outer 
  edge 
  (which 
  is 
  rounded 
  off) 
  of 
  the 
  hinge. 
  

   Suspecting 
  that 
  all 
  these 
  may 
  form 
  one 
  and 
  the 
  same 
  set, 
  we 
  pro- 
  

   pose 
  to 
  call 
  them 
  subcardinal 
  scars. 
  

  

  The 
  brachial 
  valve 
  of 
  Monomerella 
  and 
  Dinobolus 
  equally 
  shows 
  in 
  

   a 
  similar 
  position 
  (that 
  is, 
  in 
  front 
  of 
  and 
  below 
  the 
  middle 
  of 
  the 
  

   crown 
  of 
  the 
  crescent, 
  or 
  near 
  the 
  centre 
  of 
  the 
  umbonal 
  cavity) 
  a 
  

   well-marked 
  impression 
  (figs. 
  4 
  & 
  6, 
  w). 
  There 
  are 
  faint 
  indica- 
  

   tions 
  of 
  the 
  same 
  scar 
  in 
  Trimerella 
  ohioensis 
  (PI. 
  XVI. 
  figs. 
  5 
  & 
  6). 
  

  

  Trimerella 
  and 
  Monomerella 
  have 
  in 
  their 
  pedicle-valve 
  a 
  pair 
  of 
  

   umbo-lateral 
  scars 
  (x, 
  figs. 
  1 
  & 
  3), 
  a 
  member 
  being 
  situated 
  close 
  to 
  

   and 
  below 
  each 
  cardinal 
  callosity 
  (e). 
  An 
  apparently 
  corresponding 
  

   set, 
  but 
  slightly 
  marked, 
  occurs 
  in 
  Dinobolus 
  (x, 
  fig. 
  5), 
  occupying 
  a 
  

   somewhat 
  similar 
  position. 
  

  

  The 
  brachial 
  valve 
  of 
  Monomerella 
  exhibits 
  an 
  analogous 
  pair 
  

   (fig. 
  4, 
  od) 
  within 
  the 
  crescent, 
  a 
  member 
  being 
  situated 
  close 
  to 
  

   each 
  of 
  its 
  sides. 
  

  

  III. 
  Myology 
  and 
  other 
  Characters 
  of 
  the 
  Family. 
  

  

  "We 
  shall 
  now 
  offer 
  some 
  suggestions 
  as 
  to 
  which 
  organs 
  the 
  

   various 
  scars 
  respectively 
  belonged 
  to 
  ; 
  but 
  before 
  proceeding 
  further 
  

   we 
  find 
  it 
  necessary 
  to 
  anticipate 
  a 
  point 
  which 
  will 
  be 
  treated 
  of 
  in 
  

   another 
  section. 
  

  

  Having 
  failed 
  in 
  making 
  out 
  any 
  satisfactory 
  resemblance 
  be- 
  

   tween 
  the 
  Trimerellids 
  and 
  Terebratulids 
  in 
  their 
  internal 
  parts, 
  

   we 
  were 
  led 
  to 
  extend 
  our 
  investigations 
  to 
  another 
  family. 
  It 
  was 
  

   with 
  this 
  object 
  that 
  one 
  of 
  us 
  entered 
  upon 
  an 
  examination 
  of 
  the 
  

   various 
  muscles, 
  and 
  scars 
  belonging 
  to 
  them, 
  that 
  characterize 
  Lin- 
  

   gula 
  anatina*. 
  The 
  result 
  has 
  been 
  attended 
  with 
  much 
  more 
  

   success 
  than 
  in 
  the 
  case 
  of 
  the 
  Terebratulids. 
  

  

  In 
  the 
  species 
  named, 
  the 
  valvular 
  muscles 
  are 
  of 
  two 
  kinds, 
  

   direct 
  and 
  slanting. 
  The 
  direct 
  muscles 
  are 
  an 
  anterior 
  pair, 
  situ- 
  

   ated 
  in 
  the 
  central 
  region 
  of 
  the 
  shell, 
  and 
  a 
  single 
  one, 
  lodged 
  in 
  

   the 
  umbonal 
  cavity. 
  The 
  slanting 
  muscles 
  are 
  four 
  pairs 
  : 
  — 
  one 
  pair, 
  

  

  * 
  Annals 
  and 
  Mag. 
  of 
  Nat. 
  Hist. 
  4th 
  ser. 
  vol. 
  xii. 
  July 
  1873. 
  When 
  speaking 
  

   of 
  the 
  muscles 
  and 
  other 
  parts 
  of 
  Lingula 
  anatina, 
  our 
  references 
  will 
  be 
  made 
  

   to 
  the 
  figures 
  in 
  Plate 
  II. 
  accompanying 
  that 
  paper. 
  Sketches 
  after 
  the 
  two 
  

   principal 
  figures 
  are 
  given 
  in 
  the 
  annexed 
  woodcuts 
  in 
  the 
  following 
  page. 
  

  

  