﻿1058 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  In 
  the 
  brachial 
  valve 
  the 
  dental 
  sockets 
  are 
  quite 
  deep 
  and 
  

   narrow, 
  the 
  socket-walls 
  rising 
  abruptly, 
  though 
  not 
  attaining 
  

   the 
  height 
  of 
  the 
  dental 
  plates 
  of 
  the 
  opposite 
  valve. 
  They 
  are 
  

   distinctly 
  separated 
  from 
  the 
  crural 
  plates 
  or 
  

   margins 
  of 
  the 
  hinge-plate, 
  and 
  converge 
  toward 
  

   the 
  apex, 
  where 
  they 
  merge 
  into 
  a 
  slightly 
  elevated 
  

   cardinal 
  process 
  ; 
  the 
  latter 
  usually 
  appearing 
  

   Z™bot?den 
  D 
  st 
  Mort 
  as 
  a 
  crescentic 
  submarginal 
  wall, 
  though 
  when 
  

   ton. 
  An 
  eniarg- 
  best 
  preserved 
  is 
  seen 
  to 
  be 
  composed 
  of 
  two 
  

   bonT* 
  portion™^ 
  lateral, 
  somewhat 
  rounded 
  lobes. 
  The 
  crural 
  

   the 
  brachial 
  vaive, 
  plates 
  are 
  two 
  divergent 
  vertical 
  lamellae, 
  origin- 
  

   fyThicklned 
  1 
  'jko- 
  ating 
  just 
  below 
  the 
  cardinal 
  process, 
  and 
  attain- 
  

   cessesoaeitherside 
  m 
  g 
  a 
  length 
  equal 
  to 
  the 
  distance 
  between 
  their 
  

   extremities, 
  which 
  is 
  about 
  one-third 
  the 
  width 
  of 
  

   the 
  valve 
  at 
  that 
  point. 
  Between 
  these 
  plates 
  lies 
  the 
  long, 
  

   shallow 
  hinge-plate, 
  which 
  is 
  raised 
  but 
  little 
  above 
  the 
  bottom 
  

   of 
  the 
  valve, 
  and 
  is 
  sometimes 
  actually 
  adherent 
  to 
  it. 
  This 
  

   plate 
  attains 
  its 
  greatest 
  width 
  at 
  the 
  extremities 
  of 
  the 
  vertical 
  

   crural 
  plates, 
  its 
  margins 
  converging 
  thence 
  anteriorly, 
  its 
  full 
  

   length 
  often 
  equaling 
  one-third 
  that 
  of 
  

   the 
  valve. 
  To 
  this 
  plate 
  are 
  attached 
  all 
  

   the 
  muscles 
  of 
  the 
  brachial 
  valve, 
  the 
  

   scars 
  of 
  both 
  anterior 
  and 
  posterior 
  

   adductors 
  being 
  frequently 
  clearly 
  de- 
  

   fined 
  upon 
  its 
  surface. 
  The 
  lateral 
  

   divisions 
  of 
  the 
  plate 
  have 
  become 
  

   merged 
  with 
  the 
  valve 
  and 
  lost. 
  The 
  

   median 
  division, 
  which 
  is 
  also 
  to 
  a 
  cer- 
  

   tain 
  extent 
  my 
  if 
  erous 
  in 
  Ckyp 
  i 
  onella, 
  

   is 
  carried 
  to 
  an 
  extreme 
  of 
  develop- 
  

   ment 
  in 
  Dielasma, 
  where 
  it 
  forms 
  a 
  

   distinct 
  platform. 
  The 
  crura 
  are 
  

   greatly 
  abbreviated. 
  The 
  descending 
  

   lamellae 
  of 
  the 
  brachidium 
  are 
  attached 
  

   to, 
  and 
  are 
  continuous 
  with 
  the 
  crural 
  plates, 
  as 
  far 
  as 
  the 
  latter 
  

   extend. 
  The 
  crural 
  apophyses 
  on 
  the 
  upper 
  margins 
  of 
  these 
  

   lamellae 
  are 
  developed 
  behind 
  the 
  points 
  where 
  the 
  lower 
  

   margins 
  of 
  the 
  lamellae 
  are 
  free 
  from 
  the 
  crural 
  plates. 
  The 
  

   lateral 
  parts 
  of 
  the 
  brachidium 
  are 
  more 
  or 
  less 
  divergent, 
  

   the 
  recurvature 
  of 
  the 
  ascending 
  lamellae 
  rather 
  short 
  and 
  the 
  

  

  116 
  

  

  Fig. 
  501. 
  Dielasma 
  elongatum, 
  

   Schlothelm. 
  The 
  Interior 
  of 
  the 
  

   umbonal 
  region 
  of 
  the 
  two 
  valves, 
  

   showing 
  the 
  highly 
  developed 
  

   dental 
  plates 
  (d), 
  the 
  elongate, 
  

   sessile 
  hinge- 
  plate 
  with 
  its 
  muscular 
  

   scars, 
  and 
  the 
  form 
  and 
  mode 
  of 
  

   attachment 
  of 
  the 
  brachidium. 
  

   (Davidson.) 
  

  

  