﻿170 
  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TEIMERELLIDJi:. 
  

  

  margins), 
  the 
  part 
  r 
  (side 
  of 
  the 
  crescent) 
  corresponds 
  to 
  the 
  same 
  part 
  

   in 
  Trimerella 
  and 
  3Ionomerella, 
  except 
  that 
  its 
  inner 
  boundary 
  is 
  much 
  

   thicker, 
  and 
  has 
  a 
  compound 
  structure 
  : 
  probably 
  the 
  inner 
  portion 
  of 
  

   the 
  deep 
  impression 
  situated 
  at 
  the 
  angle, 
  near 
  the 
  hinge, 
  is 
  the 
  homo- 
  

   logue 
  of 
  the 
  scar, 
  at, 
  in 
  Monomerella, 
  fig. 
  4. 
  The 
  sides 
  of 
  the 
  crescent, 
  

   as 
  represented 
  in 
  fig. 
  5 
  (pedicle- 
  valve), 
  may 
  not 
  be 
  strictly 
  accurate. 
  

  

  7. 
  Area 
  and 
  hinge 
  of 
  pedicle-valve 
  of 
  Trimerella. 
  

  

  8. 
  Medio-longitudinal 
  section 
  of 
  the 
  area, 
  hinge, 
  platform, 
  and 
  median 
  plate 
  

  

  of 
  pedicle-valve 
  of 
  the 
  same 
  genus, 
  i, 
  wmbonal 
  chamber 
  on 
  left 
  side 
  

   of 
  the 
  cardinal 
  buttress, 
  h 
  ; 
  k, 
  platform 
  vault 
  on 
  left 
  side 
  of 
  the 
  median 
  

   plate, 
  1. 
  

  

  Plate 
  XIII. 
  

  

  Fig. 
  1. 
  Trimerella 
  ivisbyensis, 
  n. 
  sp. 
  Interior 
  of 
  the 
  brachial 
  valve, 
  from 
  a 
  

   gutta-percha 
  squeeze 
  taken 
  from 
  an 
  internal 
  cast. 
  Wisby 
  strata 
  ( 
  = 
  

   Wenlock), 
  near 
  Wisby, 
  Gotland. 
  

   2. 
  Trimerella 
  grandis, 
  Billings. 
  2, 
  internal 
  cast 
  of 
  pedicle-valve 
  (minus 
  

   the 
  beak) 
  : 
  2 
  a, 
  internal 
  cast 
  of 
  brachial 
  valve 
  : 
  2 
  b, 
  interior 
  of 
  brachial 
  

   valve 
  : 
  2 
  e, 
  restoration 
  of 
  the 
  pedicle 
  valve 
  : 
  3, 
  natural 
  cast 
  of 
  pedicle 
  

   valve. 
  G-uelph 
  limestone 
  (Upper 
  Silurian), 
  Hespelar, 
  Canada. 
  

  

  Plate 
  XIV. 
  

  

  Figs. 
  1, 
  la, 
  16. 
  Trimerella 
  Lindstrcemi, 
  Dall. 
  Exterior 
  of 
  a 
  large 
  specimen. 
  Cen- 
  

   tral 
  Gotland 
  (Aymestry 
  limestone), 
  Klinteberg, 
  Gotland. 
  

  

  2. 
  . 
  Interior 
  of 
  pedicle-valve. 
  Wialmsudd, 
  Gotland. 
  

  

  3. 
  . 
  Interior 
  of 
  brachial 
  valve. 
  Klinteberg, 
  Gotland. 
  

  

  4. 
  . 
  Restored 
  longitudinal 
  section 
  of 
  both 
  valves. 
  

  

  5. 
  . 
  Fragment 
  of 
  a 
  pedicle-valve, 
  showing 
  the 
  deep 
  depression 
  

  

  below 
  the 
  hinge. 
  

  

  6. 
  . 
  Transverse 
  section 
  across 
  both 
  valves. 
  

  

  7. 
  . 
  Internal 
  cast 
  of 
  the 
  brachial 
  valve. 
  Island 
  of 
  Faro. 
  Col- 
  

   lection 
  of 
  Herr 
  Fegrceus. 
  The 
  projections 
  on 
  each 
  side 
  of 
  the 
  poste- 
  

   rior 
  end 
  are 
  casts 
  of 
  umbonal 
  chambers, 
  

  

  Plate 
  XV. 
  

  

  Figs. 
  1, 
  1 
  a, 
  I, 
  c, 
  d, 
  e. 
  Trimerella 
  Dalli, 
  n. 
  sp. 
  From 
  an 
  internal 
  cast. 
  Guelph 
  

   limestone, 
  Hespelar, 
  Ontario. 
  1, 
  cast 
  of 
  pedicle-valve 
  ; 
  la, 
  of 
  brachial 
  

   valve 
  ; 
  16, 
  of 
  both 
  valves 
  in 
  conjunction 
  ; 
  lc, 
  interior 
  of 
  pedicle-valve, 
  

   from 
  a 
  gutta-percha 
  squeeze 
  ; 
  1 
  d, 
  n, 
  vaults, 
  exposed 
  under 
  platform 
  ; 
  

   M, 
  umbonal 
  cavities, 
  separated 
  by 
  the 
  cardinal 
  buttress, 
  seen 
  in 
  fig. 
  1 
  c 
  ; 
  

   le, 
  interior 
  of 
  brachial 
  valve, 
  — 
  N, 
  one 
  of 
  the 
  platform 
  vaults. 
  

  

  2. 
  . 
  Interior 
  of 
  brachial 
  valve, 
  showing 
  cardinal 
  process. 
  Same 
  

  

  formation 
  and 
  locality. 
  

  

  3, 
  3 
  a, 
  b. 
  . 
  Internal 
  cast, 
  tolerably 
  perfect, 
  in 
  the 
  Museum 
  of 
  the 
  

  

  Geological 
  Survey 
  of 
  Montreal 
  : 
  a, 
  brachial 
  valve 
  ;. 
  3, 
  pedicle-valve. 
  

  

  4, 
  4 
  a, 
  b, 
  c. 
  T. 
  acuminata, 
  Billings. 
  Internal 
  cast 
  of 
  both 
  valves 
  in 
  conjunc- 
  

   tion, 
  from 
  the 
  Guelph 
  limestone, 
  Hespelar, 
  Ontario 
  : 
  Museum 
  of 
  Mon- 
  

   treal. 
  4 
  d, 
  mould 
  in 
  gutta 
  percha 
  taken 
  from 
  the 
  umbonal 
  region 
  of 
  

   same 
  cast, 
  showing 
  the 
  cardinal 
  process 
  projecting 
  into 
  the 
  interior 
  of 
  

   the 
  shell 
  and 
  towards 
  the 
  pedicle- 
  (upper) 
  valve. 
  

  

  5. 
  . 
  Internal 
  cast 
  of 
  pedicle-valve, 
  with 
  one 
  of 
  the 
  projections 
  

  

  (cast 
  of 
  platform-vault) 
  broken. 
  

  

  6. 
  . 
  Internal 
  cast 
  of 
  a 
  pedicle-valve, 
  from 
  original 
  example 
  

  

  figured 
  in 
  1862. 
  Hespelar 
  ; 
  Museum 
  of 
  Montreal. 
  The 
  three 
  lines 
  

   are 
  furrows 
  defining 
  two 
  long 
  platform-vaults. 
  

  

  7, 
  7 
  a. 
  . 
  7, 
  internal 
  cast 
  ; 
  7 
  a, 
  gutta-percha 
  squeeze, 
  slightly 
  

  

  restored 
  at 
  the 
  margin. 
  Guelph 
  limestone 
  (Upper 
  Silurian), 
  Hespelar, 
  

   Canada 
  ; 
  Museum 
  of 
  Montreal. 
  

  

  