﻿^°1' 
  53-] 
  FAUNA 
  OF 
  THE 
  KEISLEY 
  LIMESTONE. 
  71 
  

  

  Rafinesqtjina 
  deltoidea, 
  Dalman. 
  

  

  The 
  typical 
  form 
  of 
  this 
  species 
  occurs 
  at 
  Keisley, 
  and 
  perhaps 
  at 
  

   Kildare, 
  but 
  is 
  rare. 
  It 
  is 
  recorded 
  from 
  Stage 
  E 
  of 
  the 
  East 
  Baltic 
  

   provinces 
  by 
  Schmidt. 
  1 
  

  

  Rafinesqtjina 
  (?) 
  deltoidea, 
  var. 
  tjndata, 
  M'Coy. 
  

  

  This 
  variety 
  is 
  not 
  uncommon 
  at 
  Kildare 
  and 
  Keisley. 
  I 
  strongly 
  

   doubt 
  whether 
  it 
  is 
  really 
  a 
  variety 
  of 
  R. 
  deltoidea 
  and 
  not 
  a 
  distinct 
  

   species 
  belonging 
  to 
  another 
  genus. 
  Lindstrom 
  2 
  figures 
  and 
  de- 
  

   scribes 
  a 
  variety 
  of 
  Stropheodonta 
  imbrex 
  (Pander) 
  which 
  seems 
  to 
  be 
  

   almost 
  identical 
  with 
  the 
  Keisley 
  form. 
  The 
  latter 
  agrees 
  best 
  with 
  

   fig. 
  23, 
  pi. 
  xxxix. 
  vol. 
  iii. 
  of 
  Davidson's 
  ' 
  Monograph 
  of 
  the 
  British 
  

   Fossil 
  Brachiopoda.' 
  The 
  Swedish 
  specimens, 
  however, 
  which 
  are 
  

   from 
  the 
  Leptcena- 
  Limestone 
  appear 
  to 
  be 
  less 
  suddenly 
  geniculated 
  

   and 
  to 
  possess 
  a 
  greater 
  number 
  of 
  larger 
  ribs 
  than 
  those 
  from 
  

   Keisley 
  and 
  Kildare. 
  

  

  Tkiplecia 
  insulakis, 
  Eichwald. 
  

  

  This 
  species 
  occurs 
  at 
  Keisley, 
  Kildare, 
  and 
  in 
  Stage 
  E. 
  

  

  STKEPTIS 
  MONIL1FEKA, 
  M'Coy. 
  

  

  This 
  form 
  appears 
  to 
  be 
  almost 
  restricted 
  to 
  Keisley 
  and 
  Kildare, 
  

   where 
  it 
  is 
  abundant. 
  

  

  ClEKISTIANIA 
  TENUICINCTA, 
  M'Coy. 
  

  

  This 
  is 
  a 
  very 
  common 
  species 
  at 
  Keisley, 
  and 
  is 
  also 
  found 
  at 
  

   Kildare. 
  The 
  peculiar 
  internal 
  structure 
  and 
  muscular 
  impressions 
  

   have 
  recently 
  led 
  Messrs. 
  Hall 
  & 
  Clarke 
  to 
  establish 
  the 
  new 
  genus 
  

   Christiania 
  for 
  the 
  reception 
  of 
  this 
  species, 
  which 
  previously 
  was 
  

   called 
  a 
  Leptcena. 
  

  

  Atrypa 
  expansa, 
  Lindstrom. 
  

  

  This 
  species 
  3 
  is 
  very 
  variable, 
  but 
  is 
  distinguished 
  from 
  A. 
  mar- 
  

   ginalis 
  (Dalm.) 
  by 
  its 
  subquadrate 
  form 
  and 
  diminished 
  prominence 
  

   of 
  the 
  beak 
  of 
  the 
  ventral 
  valve. 
  Three 
  fairly 
  distinct 
  varieties 
  

   occur 
  in 
  the 
  Keisley 
  Limestone. 
  The 
  first 
  (var. 
  a) 
  is 
  characterized 
  

   by 
  the 
  almost 
  obsolete 
  fold 
  on 
  the 
  brachial 
  valve, 
  while 
  the 
  sinus 
  on 
  

   the 
  pedicle-valve 
  is 
  fairly 
  strong. 
  The 
  marginal 
  fringes 
  to 
  the 
  

   valves, 
  such 
  as 
  Davidson 
  figured 
  in 
  the 
  case 
  of 
  A. 
  reticularis, 
  are 
  

   frequently 
  preserved. 
  

  

  The 
  second 
  variety 
  (/3) 
  has 
  the 
  fold 
  on 
  the 
  brachial 
  valve 
  distinct, 
  

   but 
  the 
  ribs 
  on 
  the 
  valves 
  are 
  much 
  smaller 
  and 
  more 
  numerous 
  

   than 
  in 
  the 
  type-form. 
  Thus 
  I 
  have 
  counted 
  as 
  many 
  as 
  ten 
  ribs 
  

   on 
  the 
  brachial 
  fold 
  of 
  one 
  specimen. 
  The 
  marginal 
  fringes 
  are 
  often 
  

   present 
  in 
  this 
  variety 
  also. 
  The 
  third 
  variety 
  (y) 
  is 
  characterized 
  

   by 
  the 
  possession 
  of 
  a 
  strong 
  angular 
  sinus 
  in 
  the 
  pedicle-valve, 
  

  

  1 
  'Eev. 
  d. 
  ostbalt. 
  Silur. 
  Trilob.,' 
  pt. 
  i. 
  Mem. 
  Acai 
  Imp. 
  des 
  Sci. 
  

   St, 
  Petersbourg, 
  ser. 
  7, 
  vol. 
  xxx. 
  (1881) 
  no. 
  1, 
  p. 
  38. 
  

  

  2 
  ' 
  Fragm. 
  Silur.' 
  (38SO) 
  p. 
  29, 
  pi. 
  xiv. 
  figs. 
  27-32. 
  

  

  3 
  Ibid. 
  p. 
  22, 
  pi. 
  xii. 
  figs. 
  6-10, 
  17-19. 
  

  

  