﻿172 
  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMEEELLID^. 
  

  

  Figs. 
  7, 
  7 
  a. 
  Dinobolus 
  Davidsoni. 
  7, 
  internal 
  cast 
  of 
  pedicle-valve 
  : 
  7 
  a, 
  interior 
  

   of 
  same 
  valve 
  taken 
  in 
  gutta-percha 
  from 
  internal 
  cast. 
  Wenlock, 
  

   Dudley. 
  Dudley 
  Museum. 
  

  

  8, 
  8 
  a. 
  . 
  8, 
  internal 
  cast 
  of 
  brachial 
  valve. 
  8 
  a, 
  interior 
  of 
  same 
  

  

  valve 
  from 
  a 
  gutta-percha 
  mould 
  taken 
  from 
  same 
  specimen 
  : 
  the 
  two 
  

   valves 
  are 
  in 
  juxtaposition 
  in 
  the 
  cast. 
  

  

  9. 
  . 
  Interior 
  of 
  pedicle-valve. 
  This 
  specimen, 
  which 
  shows 
  no 
  

  

  undercut 
  under 
  the 
  platform, 
  is 
  taken 
  in 
  gutta-percha 
  from 
  an 
  internal 
  

   cast. 
  Dudley. 
  In 
  the 
  Museum 
  of 
  Practical 
  Geology, 
  London. 
  

  

  11,11a. 
  . 
  Internal 
  cast 
  : 
  from 
  the 
  " 
  Central 
  Gotland" 
  ( 
  = 
  Wen- 
  

   lock) 
  of 
  the 
  neighbourhood 
  of 
  Wisby, 
  Gotland. 
  

  

  12. 
  transversus, 
  Salter. 
  Internal 
  cast 
  of 
  brachial 
  valve. 
  Top 
  of 
  Wen- 
  

   lock, 
  Dudley. 
  Dudley 
  Museum. 
  

  

  13. 
  Trimerella 
  galtensis, 
  Bill., 
  sp. 
  Interior 
  of 
  pedicle-valve. 
  Guelph 
  

   limestone, 
  Gait, 
  West 
  Canada. 
  Collection 
  of 
  Prof. 
  Hall. 
  

  

  14, 
  14 
  a, 
  b, 
  c, 
  d. 
  Chelodes 
  Bergmani, 
  n. 
  g. 
  et 
  n. 
  sp. 
  The 
  tooth-like 
  process 
  

   in 
  the 
  centre 
  of 
  what 
  appears 
  to 
  be 
  the 
  hinge 
  is 
  not 
  represented. 
  " 
  Cen- 
  

   tral 
  Gotland" 
  ( 
  = 
  Ayrnestry 
  limestone), 
  Klinteberg, 
  Gotland. 
  Collec- 
  

   tion 
  of 
  Herr 
  Bergman. 
  

  

  Plate 
  XIX. 
  

  

  Fig- 
  1. 
  Trimerella 
  oMoensis, 
  Meek. 
  Exterior 
  of 
  brachial 
  valve 
  j 
  showing 
  also 
  

   area 
  and 
  deltidium 
  of 
  pedicle-valve. 
  

  

  2. 
  . 
  Internal 
  cast 
  of 
  pedicle-valve. 
  Upper 
  Silurian, 
  Otwa, 
  

  

  Ohio 
  county. 
  After 
  drawings 
  by 
  Mr. 
  Whitfield, 
  communicated 
  by 
  

   Prof. 
  Hall. 
  

  

  3, 
  3 
  a. 
  ? 
  Monomerella 
  Wahnstedti. 
  3, 
  internal 
  cast 
  of 
  pedicle-valve 
  : 
  the 
  

  

  projections 
  are 
  casts 
  of 
  umbonal 
  chambers 
  : 
  3 
  a, 
  internal 
  cast 
  of 
  brachial 
  

   valve. 
  Tipper 
  Silurian, 
  Kerkaw, 
  Livonia, 
  Russia. 
  After 
  MS. 
  draw- 
  

   ings 
  by 
  the 
  late 
  Prof. 
  Pander, 
  communicated 
  by 
  Prof. 
  Schmidt. 
  

  

  4, 
  4 
  a. 
  Trimerella 
  galtensis, 
  Bill., 
  sp. 
  4, 
  internal 
  cast 
  of 
  brachial 
  valve 
  ; 
  

  

  4 
  a, 
  interior 
  of 
  same, 
  enlarged. 
  Upper 
  Silurian, 
  Gait, 
  Canada. 
  Mu- 
  

   seum 
  of 
  Montreal. 
  

  

  5, 
  6. 
  Dinobolus 
  Schmidti, 
  n. 
  sp. 
  ? 
  Pedicle-valve 
  : 
  internal 
  casts. 
  Lower 
  

  

  Silurian; 
  Kuna, 
  Esthonia, 
  Russia. 
  From 
  specimens 
  forwarded 
  by 
  

   Prof. 
  P. 
  Schmidt 
  ; 
  and 
  the 
  only 
  two 
  examples 
  of 
  the 
  genus 
  hitherto 
  

   found 
  in 
  Russia. 
  

  

  7. 
  Dinobolus 
  canadensis, 
  Bill., 
  sp. 
  After 
  a 
  figure 
  published 
  by 
  Mr. 
  Bil- 
  

  

  lings. 
  Trenton 
  or 
  Black-river 
  limestone. 
  Lower 
  Silurian, 
  Canada. 
  

   Museum 
  of 
  Montreal. 
  

  

  8. 
  Dinobolus 
  magnificus, 
  Bill., 
  sp. 
  After 
  a 
  figure 
  published 
  by 
  Mr. 
  Billings. 
  

  

  Same 
  locality 
  and 
  museum. 
  

  

  9. 
  9 
  a. 
  Lingulops 
  Whitfieldi, 
  J. 
  Hall. 
  9, 
  natural 
  size 
  : 
  9 
  a, 
  interior 
  of 
  

  

  brachial 
  (?) 
  valve, 
  much 
  enlarged. 
  Lower 
  Silurian, 
  United 
  States, 
  

   America. 
  Collection 
  of 
  Prof. 
  J. 
  Hall. 
  

  

  Discussion. 
  

  

  Mr. 
  Hicks 
  remarked 
  that 
  the 
  oldest 
  known 
  Lingulid 
  is 
  Lingulella 
  

   primceva. 
  The 
  Lingulce 
  in 
  the 
  earliest 
  rocks 
  increase 
  in 
  size 
  as 
  they 
  

   approach 
  shallow 
  deposits 
  ; 
  and 
  higher 
  up, 
  namely 
  in 
  the 
  Lingula- 
  

   flags, 
  a 
  change 
  takes 
  place 
  in 
  their 
  form. 
  In 
  the 
  Menevian 
  beds, 
  

   which 
  were 
  deposited 
  in 
  a 
  deep 
  sea, 
  the 
  shells 
  are 
  small. 
  Mr. 
  Hicks 
  

   thought, 
  therefore, 
  that 
  we 
  must 
  admit 
  these 
  changes 
  to 
  be 
  due 
  to 
  

   changes 
  in 
  the 
  conditions 
  of 
  existence. 
  The 
  Lingulce 
  had 
  been 
  

   declared 
  to 
  be 
  allied 
  to 
  the 
  Annelids 
  ; 
  the 
  Trilobites 
  were 
  also 
  allied 
  

   to 
  the 
  Annelids 
  ; 
  and 
  these 
  three 
  are 
  the 
  earliest 
  known 
  forms 
  of 
  

  

  