﻿1034 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  centric 
  lines. 
  Interior 
  with 
  a 
  spondylium 
  in 
  each 
  valve 
  as 
  in 
  

   parastrophia 
  ; 
  that 
  of 
  the 
  pedicle- 
  valve 
  is 
  the 
  wider 
  and 
  is 
  

   supported 
  by 
  a 
  median 
  septum 
  near 
  its 
  anterior 
  extremity. 
  

   In 
  the 
  brachial 
  valve 
  the 
  convergent 
  plates 
  generally 
  rest 
  

   upon 
  the 
  inner 
  surface 
  of 
  the 
  shell, 
  though 
  sometimes 
  the 
  

   spondylium 
  is 
  supported 
  at 
  its 
  anterior 
  extremity. 
  The 
  crural 
  

   plates 
  are 
  extravagantly 
  developed, 
  forming 
  two 
  broad 
  wing- 
  

   shaped 
  vertical 
  expansions, 
  concave 
  on 
  their 
  outer 
  surfaces; 
  

   their 
  upper 
  edges 
  are 
  curved 
  over 
  the 
  hinge-line, 
  their 
  anterior 
  

   edges 
  broadly 
  notched, 
  and 
  below 
  this 
  point 
  appears 
  the 
  base 
  

   of 
  attachment 
  for 
  the 
  crura; 
  the 
  walls 
  of 
  the 
  spondylium 
  

   being 
  connected 
  with 
  them 
  at 
  the 
  most 
  convex 
  point 
  of 
  their 
  

   inner 
  surfaces. 
  The 
  dental 
  pockets 
  are 
  always 
  small, 
  and 
  old 
  

   shells 
  frequently 
  show 
  a 
  false 
  foramen 
  in 
  the 
  beak, 
  which 
  is 
  

   simply 
  an 
  extension 
  of 
  the 
  spondylium 
  that 
  does 
  not 
  appear 
  

   to 
  be 
  accidental. 
  The 
  muscular 
  impressions 
  of 
  this 
  valve 
  are 
  

   frequently 
  denned 
  as 
  a 
  fourfold 
  scar 
  about 
  the 
  anterior 
  end 
  

   of 
  the 
  spondylium 
  ; 
  in 
  the 
  pedicle-valve 
  these 
  impressions 
  are 
  

   rarely 
  discernible. 
  

  

  Type, 
  AnastropMa 
  Verneuili, 
  Hall 
  (Lower 
  Helderberg) 
  

   Distribution. 
  Upper 
  Silurian 
  — 
  Lower 
  Devonian. 
  

  

  Porambonites, 
  Pander. 
  1830. 
  

   (Plate 
  45, 
  figs. 
  36-38.) 
  

  

  Synonym; 
  Isorhynchus, 
  King, 
  1850. 
  

  

  Shells 
  robust, 
  transverse 
  or 
  elongate, 
  sometimes 
  distinctly 
  

   triangular 
  and 
  globose. 
  Yalves 
  unequally 
  convex, 
  the 
  brachial 
  

   valve 
  being 
  always 
  the 
  deeper. 
  Pedicle-valve 
  with 
  a 
  sinus 
  to 
  

   which 
  there 
  is 
  not 
  always 
  a 
  corresponding 
  fold 
  on 
  the 
  opposite 
  

   valve. 
  Hinge-line 
  straight 
  ; 
  hinge-teeth 
  very 
  strong, 
  resting 
  on 
  

   a 
  broad 
  hinge-plate. 
  In 
  both 
  valves 
  is 
  a 
  small 
  obtusely 
  triangular 
  

   area, 
  which 
  is 
  higher 
  in 
  the 
  pedicle 
  than 
  in 
  the 
  brachial 
  valve. 
  

   Both 
  valves 
  with 
  a 
  broad 
  pedicle-passage, 
  never 
  closed 
  by 
  a 
  del- 
  

   tidium. 
  Sometimes 
  the 
  beak 
  of 
  the 
  brachial 
  valve 
  is 
  so 
  strongly 
  

   incurved 
  that 
  its 
  perforation 
  is 
  not 
  visible 
  from 
  outside. 
  On 
  the 
  

   lateral 
  slopes 
  is 
  a 
  more 
  or 
  less 
  strongly 
  denned 
  pseudolunule. 
  

  

  In 
  the 
  interior 
  of 
  the 
  pedicle-valve 
  are 
  two 
  long, 
  robust 
  dental 
  

   iamellae 
  which 
  rapidly 
  converge 
  and 
  unite, 
  sometimes 
  before 
  the 
  

   bottom 
  of 
  the 
  valve 
  is 
  reached, 
  then 
  forming 
  a 
  low 
  median 
  

  

  92 
  

  

  