﻿Report 
  of 
  the 
  State 
  Geologist. 
  

  

  1063 
  

  

  as 
  a 
  very 
  broad, 
  continuous 
  lamella, 
  which 
  is 
  not 
  reflexed 
  though 
  

   somewhat 
  curved 
  upward 
  on 
  the 
  anterior 
  margin. 
  From 
  the 
  

   inner 
  margins 
  of 
  this 
  lamella, 
  on 
  its 
  exterior 
  and 
  lateral 
  

  

  Fig 
  510. 
  

  

  Fig. 
  512. 
  

  

  Fig. 
  511. 
  

  

  Stringocephaius 
  Burtini, 
  Def 
  ranee. 
  

   Fig. 
  510 
  Umbonal 
  cavity 
  of 
  the 
  p9d 
  c 
  e-vaivc 
  wLh 
  discrete 
  de 
  tidial 
  plates. 
  

   Fig 
  5t 
  : 
  . 
  The 
  internal 
  sheath 
  or 
  projection 
  of 
  th^ 
  pedic 
  e-passage. 
  

  

  Fig 
  512. 
  Theumbona 
  cavi 
  y 
  of 
  a 
  peiicle- 
  valve 
  in 
  which 
  coalescence 
  of 
  the 
  deltidial 
  plates 
  

   is 
  almost 
  complete. 
  cQpenstedt.) 
  

  

  extension, 
  arises 
  a 
  series 
  of 
  linear 
  processes 
  converging 
  toward, 
  

   and 
  some 
  of 
  them 
  perhaps 
  reaching 
  the 
  crura. 
  A 
  low, 
  thick 
  

   median 
  septum 
  extends 
  for 
  about 
  half 
  the 
  length 
  of 
  the^ 
  valve. 
  

  

  Fig. 
  513. 
  Stringocephaius 
  Burtini, 
  Defrance. 
  

   A 
  restoration 
  of 
  the 
  interior, 
  show 
  ng 
  the 
  internal 
  pedicle-sheath 
  and 
  the 
  strong 
  median 
  sep- 
  

   tum 
  of 
  th. 
  pedic 
  e- 
  valve; 
  the 
  gr-at 
  cardinal 
  process, 
  one 
  of 
  its 
  terninal 
  !obe< 
  (c) 
  'ying 
  on 
  

   either 
  side 
  of 
  the 
  septuaa; 
  the 
  f 
  jm 
  of 
  the 
  loop 
  w*th 
  the 
  radial 
  filaments 
  extending 
  from 
  the 
  

   anterior 
  1 
  imellae 
  (d) 
  to 
  the 
  crura. 
  At 
  (a) 
  is 
  the 
  insertion 
  of 
  the 
  diductor 
  muscle, 
  (o) 
  that 
  of 
  

   the 
  adductor. 
  (Hokr.nks.) 
  

  

  The 
  muscular 
  impressions 
  on 
  both 
  values 
  are 
  exceedingly 
  

   obscure, 
  and 
  have 
  never 
  been 
  fully 
  described 
  or 
  illustrated. 
  

  

  Surface 
  smooth, 
  with 
  fine 
  concentric 
  growth-lines 
  ; 
  sometimes 
  

   a 
  low 
  median 
  sinus 
  exists 
  on 
  both 
  valves 
  near 
  the 
  margin. 
  

  

  121 
  

  

  