﻿150 
  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMERELLID.3J. 
  

  

  Specimens 
  of 
  this 
  remarkable 
  fossil 
  were 
  first 
  discovered 
  by 
  Dr. 
  

   Lindstrom 
  in 
  1859, 
  and 
  soon 
  afterwards 
  forwarded 
  for 
  examination 
  

   to 
  one 
  of 
  the 
  writers 
  of 
  the 
  present 
  memoir, 
  accompanied 
  by 
  a 
  MS. 
  

   description 
  and 
  figures 
  ; 
  but 
  it 
  was 
  only 
  after 
  the 
  publication 
  by 
  

   Billings 
  of 
  his 
  genus 
  Trimerella 
  in 
  1862 
  that 
  certain 
  other 
  characters 
  

   of 
  the 
  shell 
  were 
  determined 
  by 
  Dr. 
  Lindstrom. 
  His 
  material 
  being 
  

   more 
  complete 
  than 
  that 
  upon 
  which 
  the 
  genus 
  was 
  founded, 
  he 
  

   published, 
  in 
  1867, 
  a 
  description 
  and 
  figures 
  of 
  the 
  species, 
  but 
  without 
  

   giving 
  it 
  a 
  name. 
  He 
  was, 
  however, 
  mistaken 
  in 
  believing 
  that 
  the 
  

   vaulted 
  platform 
  is 
  smooth, 
  and 
  had 
  no 
  impressions 
  of 
  muscular 
  scars 
  

   upon 
  it, 
  as 
  these 
  occurred 
  to 
  us 
  very 
  plainly 
  on 
  one 
  of 
  his 
  specimens, 
  

   thus 
  confirming 
  the 
  idea 
  entertained 
  by 
  Billings 
  in 
  1862. 
  

  

  In 
  1870 
  Mr. 
  Dall, 
  from 
  not 
  quite 
  understanding 
  the 
  characters 
  of 
  

   Mr. 
  Billings's 
  genus 
  Trimerella, 
  and 
  those 
  of 
  Dr. 
  Lindstrom's 
  species, 
  

   proposed 
  for 
  this 
  last 
  a 
  new 
  generic 
  appellation, 
  Ootlandia 
  ; 
  but 
  in 
  

   1871 
  he 
  corrected 
  the 
  mistake. 
  In 
  the 
  same 
  year 
  he 
  described 
  the 
  

   species 
  under 
  the 
  designation 
  of 
  ? 
  Trimerella 
  Lindstroemi. 
  

  

  Some 
  specimens 
  have 
  been 
  found 
  three 
  inches 
  in 
  length 
  by 
  two 
  

   and 
  a 
  half 
  in 
  breadth 
  and 
  one 
  in 
  depth. 
  

  

  "We 
  are 
  informed 
  by 
  Dr. 
  Lindstrom 
  that 
  this 
  species 
  may 
  be 
  re- 
  

   garded 
  as 
  one 
  of 
  the 
  most 
  characteristic 
  fossils 
  of 
  the 
  Silurian 
  rocks 
  

   of 
  the 
  Island 
  of 
  Gotland. 
  Almost 
  everywhere 
  may 
  be 
  discerned 
  

   fragments 
  of 
  it 
  on 
  the 
  weathered 
  surface 
  of 
  the 
  limestone 
  — 
  often 
  

   transverse 
  sections 
  of 
  both 
  valves 
  ; 
  so 
  that 
  the 
  hard 
  crystalline 
  

   rock 
  seems 
  to 
  be 
  almost 
  entirely 
  made 
  up 
  of 
  them 
  — 
  to 
  such 
  an 
  

   extent 
  that 
  it 
  might 
  be 
  termed 
  the 
  " 
  Trimerella 
  limestone." 
  There 
  

   are, 
  nevertheless, 
  a 
  few 
  localities 
  where 
  tolerably 
  good 
  speci- 
  

   mens 
  may 
  be 
  collected, 
  such 
  as 
  at 
  Klinteberg, 
  Fole, 
  Iamsugnen, 
  a 
  

   limestone 
  quarry 
  in 
  the 
  parish 
  of 
  Olham, 
  at 
  Eurillen 
  on 
  the 
  east 
  

   steep 
  coast 
  of 
  Gotland, 
  "Widlansudd, 
  situated 
  quite 
  at 
  the 
  extremity 
  

   of 
  the 
  island, 
  and 
  in 
  Faro 
  on 
  the 
  north 
  coast 
  of 
  Gotland. 
  

  

  It 
  is, 
  however, 
  only 
  within 
  the 
  range 
  of 
  the 
  " 
  Central 
  Gotland 
  " 
  

   beds 
  of 
  the 
  islands 
  of 
  Gotland 
  and 
  F§,ro 
  that 
  T. 
  Lindstroemi 
  (with 
  

   T. 
  acuminata) 
  has 
  been 
  found. 
  These 
  beds 
  have 
  been 
  considered 
  

   by 
  Dr. 
  Lindstrom 
  and 
  by 
  Sir 
  B. 
  Murchison 
  equivalent 
  to 
  the 
  

   Aymestry 
  rocks 
  of 
  England, 
  a 
  view 
  fully 
  supported 
  by 
  fossil 
  evidence. 
  

   "We 
  are 
  indebted 
  to 
  Dr. 
  Lindstrom, 
  to 
  Prof. 
  E. 
  "Walmstedt 
  of 
  the 
  

   University 
  of 
  Upsala, 
  and 
  to 
  Herr 
  Fegrceus 
  for 
  many 
  specimens 
  of 
  

   this 
  species. 
  

  

  Trimerella 
  Billingsii, 
  Dall. 
  PL 
  XVI. 
  figs. 
  8 
  & 
  9. 
  

  

  Trimerella 
  Billingsii, 
  Dall, 
  Am. 
  Journal 
  of 
  Conch, 
  vol. 
  vii. 
  part 
  2, 
  

   p. 
  82, 
  pis. 
  1, 
  2, 
  1871 
  *. 
  

  

  Shell 
  longitudinally 
  oval; 
  compressed: 
  umbonal 
  region 
  projecting; 
  

   twisted 
  to 
  one 
  side. 
  Pedicle-valve 
  — 
  deltidium 
  large 
  ; 
  wide 
  ; 
  trans- 
  

   versely 
  striated 
  ; 
  slightly 
  excavated 
  ; 
  strongly 
  bordered 
  at 
  sides 
  by 
  the 
  

  

  * 
  The 
  fossil 
  referred 
  to 
  T. 
  Billinsgii 
  in 
  this 
  paper 
  was 
  so 
  labelled 
  by 
  Mr. 
  

   Dall 
  ; 
  but 
  he 
  must 
  have 
  mistaken 
  some 
  other 
  specimens 
  for 
  this 
  species, 
  as 
  the 
  

   longitudinal 
  section 
  given 
  in 
  his 
  fig. 
  3 
  appears 
  to 
  have 
  been 
  taken 
  from 
  a 
  speci- 
  

   men 
  of 
  Trimerella 
  grandis. 
  

  

  