﻿^"°L 
  53'] 
  PATT^A 
  OF 
  THE 
  KEISLEY 
  LIMESTONE. 
  69 
  

  

  Orthis 
  (Dalmanella) 
  testudinaria, 
  Dalman. 
  

  

  JSTot 
  very 
  common 
  at 
  Keisley. 
  It 
  has 
  not 
  been 
  recorded 
  so 
  far 
  

   from 
  the 
  Kildare 
  or 
  the 
  Leptcena-Limestone. 
  

  

  Orthis 
  (Dalmanella 
  ?) 
  of. 
  conferta, 
  Lindstrom. 
  

  

  Lindstrom 
  l 
  describes 
  and 
  figures 
  a 
  small 
  species 
  of 
  Orthis 
  from 
  

   Ihe 
  Z<2p 
  ^ma-Limestone 
  under 
  the 
  name 
  of 
  0. 
  conferta. 
  Some 
  

   specimens 
  from 
  Keisley 
  appear 
  to 
  belong 
  to 
  it, 
  agreeing 
  in 
  shape 
  

   -and 
  surface-ornamentation. 
  

  

  Orthis 
  of. 
  argentea, 
  Hisinger. 
  

  

  I 
  have 
  but 
  little 
  doubt 
  that 
  this 
  species 
  of 
  Hisinger's 
  2 
  occurs 
  at 
  

   Keisley, 
  for 
  several 
  well-preserved 
  shells 
  show 
  all 
  the 
  typical 
  

   external 
  features 
  with 
  the 
  regular 
  bifurcation 
  of 
  the 
  ribs, 
  but 
  they 
  

   .are 
  of 
  rather 
  large 
  size. 
  In 
  Sweden 
  it 
  occurs 
  in 
  the 
  Trinucleus- 
  

   Schists. 
  

  

  Orthis 
  (Hebertella?) 
  keisleyensis, 
  sp. 
  n. 
  (PI. 
  VI. 
  figs. 
  1, 
  1 
  a, 
  & 
  1 
  b.) 
  

  

  This 
  species 
  is 
  founded 
  on 
  a 
  single 
  pedicle-valve 
  of 
  a 
  small 
  speci- 
  

   men, 
  but 
  it 
  shows 
  characters 
  so 
  peculiar 
  and 
  distinct 
  that 
  a 
  new 
  

   specific 
  name 
  is 
  not 
  uncalled 
  for. 
  

  

  The 
  valve 
  is 
  transverse, 
  with 
  a 
  semicircular 
  outline. 
  The 
  depth 
  

   at 
  the 
  umbo 
  is 
  nearly 
  one-third 
  of 
  the 
  total 
  length. 
  There 
  is 
  a 
  

   very 
  faint 
  indication 
  of 
  a 
  median 
  sinus 
  ; 
  the 
  beak 
  is 
  small, 
  and 
  not 
  

   curved 
  over 
  the 
  hinge-line. 
  

  

  The 
  hinge-line 
  is 
  straight, 
  and 
  there 
  is 
  a 
  high, 
  triangular, 
  steeply 
  

   inclined 
  hinge- 
  area. 
  The 
  surface 
  of 
  the 
  valve 
  is 
  ornamented 
  with 
  

   about 
  sixteen 
  simple, 
  straight, 
  unforked, 
  narrow, 
  rounded 
  ribs 
  

   extending 
  from 
  the 
  beak 
  to 
  the 
  margin, 
  with 
  interspaces 
  of 
  quite 
  

   double 
  the 
  width 
  of 
  the 
  ribs. 
  

  

  The 
  ribs 
  and 
  interspaces 
  are 
  crossed 
  by 
  strong, 
  rounded, 
  raised, 
  

   equidistant, 
  concentric 
  lines, 
  not 
  lamellose 
  ; 
  these 
  give 
  a 
  distinct 
  

   cancellated 
  appearance 
  to 
  the 
  surface. 
  

  

  The 
  length 
  of 
  the 
  valve 
  is 
  5 
  millim., 
  and 
  its 
  width 
  6 
  millim. 
  

  

  In 
  the 
  shape 
  of 
  the 
  pedicle-valve 
  and 
  the 
  characters 
  of 
  the 
  hinge- 
  

   area, 
  this 
  Keisley 
  form 
  resembles 
  the 
  species 
  belonging 
  to 
  the 
  group 
  

   Hebertella 
  of 
  Hall 
  & 
  Clarke, 
  3 
  but 
  none 
  of 
  the 
  species, 
  so 
  far 
  as 
  I 
  

   know, 
  have 
  a 
  precisely 
  similar 
  ornamentation. 
  

  

  In 
  these 
  respects 
  also 
  the 
  common 
  Wenlock 
  species, 
  Orthis 
  Bou- 
  

   chardi 
  (Davidson), 
  is 
  not 
  unlike 
  our 
  specimen, 
  but 
  it 
  has 
  fewer 
  ribs 
  

   and 
  the 
  concentric 
  markings 
  are 
  lamellose. 
  

  

  Orthis 
  vespertilto, 
  Sowerby. 
  

  

  There 
  is 
  a 
  specimen 
  in 
  the 
  Carlisle 
  Museum 
  from 
  Keisley, 
  but 
  it 
  

   is 
  a 
  rare 
  form. 
  It 
  probably 
  occurs 
  at 
  Kildare. 
  

  

  1 
  ' 
  Fragm. 
  Silur.' 
  (1880) 
  p. 
  26, 
  pi. 
  xiii. 
  figs. 
  1-3. 
  

  

  2 
  Ibid. 
  pi. 
  xiv. 
  figs. 
  12-15; 
  and 
  Hisinger, 
  'Lethsea 
  Suecic.i 
  ' 
  (1837), 
  p. 
  72, 
  

   j>l. 
  xx. 
  fig. 
  15. 
  

  

  3 
  « 
  Pal. 
  N. 
  Y.,' 
  vol. 
  viii. 
  Brach. 
  pt. 
  i. 
  (1892) 
  p. 
  198. 
  

  

  