﻿160 
  T. 
  DAVIDSON 
  AND 
  W. 
  KINO 
  ON 
  THE 
  TEIMEBELLIDiE. 
  

  

  of 
  subcardinal 
  scars, 
  w. 
  Brachial 
  valve 
  rather 
  tumid 
  at 
  the 
  umbo 
  : 
  

   platform 
  somewhat 
  strongly 
  trilobed; 
  its 
  outer 
  margins 
  a 
  little 
  

   raised 
  ; 
  its 
  antemedian 
  portion 
  rounded, 
  projecting, 
  and 
  terminating 
  

   in 
  a 
  slightly 
  developed 
  median 
  plate 
  : 
  crescent 
  a 
  strongly 
  marked 
  

   linear 
  scar 
  on 
  the 
  hinge 
  ; 
  arching 
  forward 
  in 
  front 
  of 
  the 
  cardinal 
  

   facet; 
  inner 
  border 
  of 
  its 
  sides 
  with 
  strongly 
  marked 
  indenta- 
  

   tions 
  — 
  one 
  near 
  the 
  hinge, 
  another 
  further 
  forward; 
  outer 
  border 
  

   a 
  fine 
  line 
  : 
  a 
  rather 
  strongly 
  marked 
  subcardinal 
  scar, 
  w, 
  in 
  the 
  

   umbonal 
  cavity 
  : 
  a 
  large 
  rhomboidal 
  postmedian 
  scar, 
  p, 
  in 
  front 
  of 
  

   the 
  latter. 
  

  

  Type 
  species, 
  Obolus 
  Conradi, 
  Hall. 
  

  

  The 
  somewhat 
  general 
  description 
  given 
  in 
  the 
  above 
  diagnosis 
  

   points 
  out 
  some 
  of 
  the 
  chief 
  differences 
  between 
  the 
  present 
  geuus 
  

   and 
  the 
  preceding 
  ones. 
  In 
  the 
  latter 
  the 
  area 
  is 
  longer 
  than 
  wide 
  ; 
  

   consequently 
  the 
  umbo 
  is 
  much 
  more 
  projecting. 
  In 
  Dinobolus 
  de- 
  

   velopment 
  of 
  the 
  valves 
  is 
  in 
  general 
  bilateral 
  rather 
  than 
  longitu- 
  

   dinal 
  ; 
  and 
  the 
  areal 
  characters 
  are, 
  as 
  a 
  consequence, 
  not 
  well 
  exhi- 
  

   bited 
  : 
  nevertheless 
  the 
  hinge 
  shows 
  the 
  crown 
  of 
  the 
  crescent 
  rather 
  

   conspicuously. 
  This 
  last 
  part 
  in 
  both 
  valves 
  differs 
  from 
  its 
  equiva- 
  

   lent 
  in 
  Trimerella 
  and 
  Monomerella 
  : 
  the 
  outer 
  border 
  of 
  its 
  sides 
  is 
  

   a 
  simple 
  line 
  which 
  runs 
  off 
  from 
  the 
  hinge 
  along 
  and 
  within 
  the 
  post- 
  

   lateral 
  margins 
  of 
  the 
  valves, 
  as 
  in 
  these 
  genera 
  ; 
  but 
  the 
  inner 
  bor- 
  

   der, 
  instead 
  of 
  also 
  being 
  a 
  simple 
  line, 
  is 
  irregular 
  in 
  width, 
  and 
  com- 
  

   posite 
  in 
  structure, 
  being 
  broad 
  and 
  strongly 
  indented 
  — 
  at 
  least 
  in 
  two 
  

   separate 
  places 
  : 
  the 
  ends 
  of 
  the 
  crescent 
  are 
  not 
  well 
  defined, 
  arising 
  

   from 
  interblending 
  growths. 
  The 
  platforms 
  nearly 
  resemble 
  those 
  

   of 
  Monomerella; 
  but 
  the 
  one 
  belonging 
  to 
  the 
  pedicle-valve 
  has 
  

   its 
  front 
  sinuated 
  (sometimes 
  five-lobed), 
  — 
  not 
  straight, 
  as 
  in 
  the 
  

   genus 
  referred 
  to. 
  The 
  umbonal 
  cavity 
  of 
  the 
  pedicle-valve 
  shows 
  

   a 
  tendency 
  to 
  become 
  double-chambered, 
  the 
  division 
  being 
  caused 
  

   by 
  a 
  slightly 
  developed 
  cardinal 
  buttress 
  (PI. 
  XVIII. 
  fig. 
  7, 
  7 
  a). 
  

   This 
  region 
  shows 
  a 
  very 
  small 
  pair 
  of 
  umbo-lateral 
  scars 
  (PI. 
  XII. 
  

   fig. 
  5x) 
  below 
  the 
  subcardinal 
  scars, 
  w, 
  already 
  noticed. 
  The 
  

   deltidium 
  and 
  other 
  parts 
  belonging 
  to 
  the 
  area 
  are 
  imperfectly 
  dis- 
  

   played 
  in 
  all 
  the 
  specimens 
  we 
  have 
  examined 
  ; 
  though 
  in 
  one 
  spe- 
  

   cies 
  (D. 
  canadense, 
  not 
  examined 
  by 
  us), 
  according 
  to 
  Mr. 
  Billings's 
  

   figure 
  of 
  it, 
  copied 
  in 
  PI. 
  XIX. 
  fig. 
  7, 
  the 
  deltidium 
  appears 
  to 
  be 
  

   well 
  developed. 
  The 
  dentary 
  system 
  is 
  probably 
  rudimentary. 
  The 
  

   platforms 
  occasionally 
  show 
  a 
  tendency 
  to 
  become 
  vaulted. 
  

  

  The 
  genus 
  embraces 
  D. 
  Conradi, 
  D. 
  Davidsoni, 
  D. 
  canadensis, 
  

   D. 
  transversus, 
  D. 
  magnificus, 
  and 
  some 
  others 
  which 
  may 
  be 
  mere 
  

   varieties. 
  

  

  Dinobolus 
  Conradi, 
  Hall. 
  PI. 
  XVIII. 
  figs. 
  1-5. 
  

  

  Obolus 
  Conradi, 
  Hall, 
  Twentieth 
  Annual 
  Eeport 
  of 
  the 
  Regents 
  

   of 
  the 
  University 
  of 
  the 
  State 
  of 
  New 
  York, 
  p. 
  368, 
  1868 
  ; 
  and 
  

   revised 
  ed., 
  p. 
  375, 
  1870. 
  

  

  Trimerella 
  Conradi, 
  Dall, 
  American 
  Journ. 
  of 
  Conch, 
  vol. 
  vii. 
  

   part 
  2, 
  p. 
  83, 
  1871. 
  

  

  Dinobolus 
  Conradi, 
  Hall, 
  Preliminary 
  Notice, 
  Twenty-third 
  Report 
  

  

  