﻿T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMEKEELIDJE. 
  161 
  

  

  on 
  the 
  State 
  Cabinet 
  of 
  New 
  York, 
  p. 
  3, 
  March 
  1872: 
  Dav. 
  & 
  

   King, 
  Report 
  of 
  the 
  Brighton 
  Meeting 
  of 
  Brit. 
  Assoc. 
  20th 
  

   August, 
  1872. 
  

  

  General 
  form 
  orbicular 
  ; 
  depressed 
  ; 
  broadly 
  rounded 
  anteriorly 
  ; 
  

   tapering 
  rapidly 
  in 
  the 
  umbonal 
  region. 
  Pedicle-valve 
  flatly 
  convex 
  : 
  

   area 
  small 
  : 
  deltidium 
  concave 
  : 
  platform 
  undulated 
  on 
  its 
  surface 
  ; 
  

   sinuated, 
  and 
  elevated 
  in 
  front: 
  cardinal 
  buttress 
  slightly 
  but 
  

   obviously 
  developed 
  : 
  crescent 
  conspicuously 
  displayed. 
  Brachial 
  

   valve 
  rather 
  tumid 
  at 
  the 
  umbo 
  : 
  platform 
  sinuated, 
  and 
  raised 
  at 
  

   the 
  sides 
  ; 
  produced, 
  and 
  depressed 
  in 
  its 
  antemedian 
  portion 
  : 
  

   median 
  plate 
  short 
  : 
  crescent 
  conspicuously 
  displayed 
  in 
  part. 
  

  

  Of 
  this 
  important 
  species 
  some 
  specimens 
  have 
  attained 
  to 
  1| 
  inch 
  

   in 
  length 
  by 
  1 
  inch 
  11 
  lines 
  in 
  width; 
  but 
  the 
  larger 
  number 
  of 
  

   specimens 
  that 
  have 
  fallen 
  under 
  our 
  notice 
  presented 
  almost 
  

   equal 
  length 
  and 
  breadth. 
  In 
  a 
  specimen 
  measuring 
  11 
  lines 
  in 
  

   length, 
  the 
  platform 
  of 
  the 
  pedicle- 
  valve 
  is 
  to 
  some 
  extent 
  doubly 
  

   vaulted, 
  the 
  vaults 
  attaining 
  two 
  lines 
  in 
  depth 
  (PI. 
  XVIII. 
  fig. 
  2, 
  ri) 
  ; 
  

   but 
  in 
  none 
  of 
  the 
  other 
  examples 
  we 
  have 
  seen 
  did 
  they 
  exceed 
  a 
  

   line 
  or 
  a 
  line 
  and 
  a 
  half. 
  

  

  Dinobolus 
  Conradi 
  occurs 
  in 
  a 
  dolomitic 
  limestone 
  belonging 
  to 
  the 
  

   upper 
  part 
  of 
  the 
  Niagara 
  group 
  ( 
  = 
  Upper 
  Silurian), 
  at 
  Leclaire, 
  

   Iowa 
  ; 
  also 
  at 
  Racine, 
  Wisconsin, 
  United 
  States 
  of 
  America. 
  

  

  Dinobolus 
  Davidsoni, 
  Salter. 
  PL 
  XVIII. 
  figs. 
  6-11. 
  

  

  Obolus 
  Davidsoni, 
  Salter, 
  MS. 
  ; 
  Woodward, 
  Manual 
  of 
  the 
  Mollusca, 
  

   p. 
  240, 
  1856 
  ; 
  Davidson, 
  Mon. 
  Brit. 
  Foss. 
  Brach. 
  vol. 
  i. 
  Intro- 
  

   duction, 
  p. 
  58, 
  pi. 
  4. 
  figs. 
  30-39,1866; 
  Salter, 
  Murchison's 
  

   Siluria, 
  2nd 
  ed. 
  p. 
  543, 
  1859 
  ; 
  Lindstrom, 
  Sil. 
  Brach. 
  of 
  Got- 
  

   land, 
  Ofversigt. 
  af. 
  K. 
  Vet. 
  Akad. 
  Fdrhandl. 
  p. 
  375, 
  1860. 
  

  

  Dinobolus 
  Davidsoni, 
  Dav. 
  & 
  King, 
  Report 
  of 
  Brighton 
  Meeting 
  

   of 
  Brit. 
  Assoc. 
  20th 
  August, 
  1872. 
  

  

  General 
  form 
  slightly 
  wider 
  than 
  long 
  ; 
  subequivalve 
  ; 
  compressed 
  : 
  

   surface 
  marked 
  with 
  concentric 
  lines 
  of 
  growth. 
  Pedicle-valve 
  

   moderately 
  convex 
  : 
  umbo 
  very 
  short 
  : 
  area 
  and 
  its 
  component 
  cha- 
  

   racters 
  small 
  : 
  crescent 
  well 
  defined 
  in 
  its 
  crown, 
  the 
  central 
  part 
  of 
  

   which 
  curves 
  forward 
  ; 
  its 
  sides 
  and 
  ends 
  complex 
  : 
  hinge 
  a 
  T-shaped 
  

   ledge, 
  the 
  top 
  branches 
  forming 
  its 
  sides, 
  and 
  the 
  perpendicular 
  

   part 
  forming 
  the 
  cardinal 
  buttress 
  : 
  platform 
  with 
  sides 
  straight, 
  and 
  

   diverging 
  from 
  its 
  posterior 
  end 
  ; 
  a 
  broad 
  sinuated 
  front 
  ; 
  and 
  a 
  

   strongly 
  undulating 
  surface. 
  Brachial 
  valve 
  moderately 
  convex: 
  

   crescent 
  well 
  defined 
  at 
  its 
  crown, 
  the 
  centre 
  of 
  which 
  is 
  pointed, 
  the 
  

   point 
  directed 
  backward 
  : 
  platform 
  trilobed 
  in 
  outline 
  ; 
  its 
  central 
  

   lobe 
  or 
  terminal 
  extremity 
  projecting, 
  and 
  depressed 
  below 
  the 
  lateral 
  

   lobes 
  : 
  close 
  behind 
  is 
  situated 
  the 
  postmedian 
  scar, 
  p, 
  which 
  is 
  

   rhomboidal 
  in 
  outline 
  : 
  further 
  behind 
  is 
  the 
  subcardinal 
  scar, 
  w. 
  

  

  This 
  species 
  occurs 
  occasionally 
  so 
  well 
  preserved 
  that 
  it 
  has 
  

   afforded 
  the 
  principal 
  characters 
  diagnosed 
  for 
  the 
  genus, 
  especially 
  

   the 
  scars 
  on 
  and 
  near 
  the 
  hinge, 
  also 
  those 
  belonging 
  to 
  the 
  platform. 
  

   The 
  crescent, 
  as 
  will 
  have 
  been 
  observed, 
  is 
  instructively 
  displayed 
  in 
  

  

  