﻿Report 
  of 
  the 
  State 
  Geologist. 
  1037 
  

  

  fully 
  one- 
  half 
  the 
  depth 
  of 
  the 
  combined 
  valves. 
  The 
  spondylium 
  

   is 
  very 
  narrow 
  and 
  deep 
  ; 
  combined 
  with 
  the 
  median 
  septum 
  the 
  

   height 
  of 
  these 
  plates 
  equals 
  fully 
  two-thirds 
  the 
  depth 
  of 
  the 
  

   valve. 
  The 
  anterior 
  margins 
  of 
  these 
  plates 
  are 
  doubly 
  incurved, 
  

   the 
  most 
  projecting 
  points 
  being 
  at 
  the 
  base 
  of 
  the 
  septum, 
  and 
  

   at 
  its 
  line 
  of 
  union 
  with 
  the 
  dental 
  lamella?. 
  The 
  median 
  

   septum 
  consists 
  of 
  two 
  vertical 
  lamellae, 
  each 
  continuous 
  

   with 
  one 
  of 
  the 
  component 
  plates 
  of 
  the 
  spondylium. 
  

   The 
  spondylium 
  was 
  the 
  seat 
  of 
  muscular 
  attachment, 
  and 
  it 
  

   bears 
  a 
  series 
  of 
  fine 
  radiating 
  lines 
  along 
  its 
  median 
  portion, 
  and 
  

   transverse 
  or 
  concentric 
  lines 
  over 
  its 
  lateral 
  slopes; 
  the 
  

   former 
  probably 
  representing 
  the 
  scar 
  of 
  the 
  adductor, 
  and 
  the 
  

  

  Fig. 
  451. 
  Fig. 
  452. 
  

  

  i 
  Fig. 
  Abi.—Pentamerus 
  (Conchidiuni) 
  Knighti. 
  A 
  transverse 
  section 
  in 
  tha 
  umbonal 
  region. 
  

   8 
  Septum 
  of 
  the 
  pedicle- 
  valve. 
  p. 
  Dantii 
  plates 
  formmg 
  ventral 
  spondylium. 
  

  

  s'. 
  Septa 
  of 
  the 
  brachial 
  valve. 
  6. 
  Crural 
  plates 
  resting 
  on 
  the 
  septa. 
  

  

  Fig 
  454.— 
  Conchidium 
  laqueatum, 
  Conrad. 
  Transverse 
  section, 
  showing 
  the 
  deflection 
  of 
  the 
  

   median 
  septum, 
  the 
  deep, 
  narrow 
  spondylium 
  of 
  the 
  pedicle- 
  valve, 
  and 
  the 
  septa 
  of 
  the 
  

   brachial 
  valve 
  bearing 
  inclined 
  crural 
  processes. 
  

  

  latter 
  the 
  impressions 
  of 
  the 
  diductor 
  muscles. 
  In 
  the 
  brachial 
  

   valve 
  the 
  beak 
  is 
  obtuse 
  and 
  closely 
  incurved 
  into 
  the 
  deltidial 
  

   cavity 
  or 
  spondylium 
  of 
  the 
  opposite 
  valve. 
  The 
  dental 
  sockets 
  

   are 
  long 
  and 
  narrow, 
  their 
  inner 
  margins 
  being 
  bordered 
  by 
  two 
  

   broad, 
  convergent 
  crural 
  plates, 
  which 
  extend 
  toward 
  the 
  bottom 
  

   of 
  the 
  valve, 
  but 
  do 
  not 
  reach 
  it. 
  These 
  sloping 
  plates 
  are 
  sup- 
  

   ported 
  by 
  two 
  vertical 
  septa, 
  with 
  which 
  they 
  are 
  united, 
  not 
  at 
  

   their 
  extremities, 
  but 
  obliquely, 
  just 
  within 
  their 
  free 
  edges. 
  

   At 
  the 
  anterior 
  angles 
  of 
  these 
  free 
  edges, 
  there 
  are 
  two 
  long, 
  

   straight 
  or 
  slightly 
  curved, 
  rod 
  like 
  crural 
  processes 
  extending 
  

   into 
  the 
  anterior 
  cavity 
  of 
  the 
  shell. 
  Beneath 
  the 
  beak 
  is 
  a 
  

   faintly 
  developed, 
  bilobate 
  or 
  multilobate 
  cardinal 
  process. 
  The 
  

   muscular 
  scars 
  lie 
  on 
  the 
  surface 
  of 
  the 
  valve 
  between 
  the 
  two 
  

  

  95 
  

  

  