﻿966 
  Forty-seventh 
  Retort 
  on 
  the 
  State 
  Museum. 
  

  

  In 
  the 
  brachial 
  valve 
  a 
  median 
  septum 
  is 
  more 
  or 
  less 
  strongly 
  

   developed 
  and 
  divides 
  a 
  simple 
  ovate 
  adductor 
  impression. 
  The 
  

   hinge-plate 
  is 
  short 
  and 
  deeply 
  divided 
  by 
  a 
  median 
  groove. 
  

   The 
  brachial 
  supports 
  consist 
  of 
  spiral 
  cones 
  with 
  their 
  bases 
  in 
  

   apposition 
  and 
  parallel 
  to 
  the 
  axial 
  plane 
  of 
  the 
  shell, 
  and 
  

   their 
  apices 
  directed 
  toward 
  the 
  lateral 
  margins. 
  The 
  jugum 
  

   has 
  been 
  shown 
  by 
  Glass 
  to 
  have 
  the 
  following 
  structure: 
  The 
  

   lateral 
  branches 
  approach 
  and 
  unite 
  near 
  the 
  middle 
  of 
  the 
  

   interior 
  cavity, 
  forming 
  a 
  very 
  short 
  stem, 
  from 
  the 
  posterior 
  

   extremity 
  of 
  which 
  is 
  given 
  off 
  a 
  pair 
  of 
  arms. 
  These 
  curve 
  

  

  Fig. 
  307.— 
  The 
  spirals 
  and 
  jugum 
  of 
  Merista 
  herculea, 
  Barrande. 
  (Davidson, 
  from 
  a 
  

   preparation 
  by 
  Glass.) 
  

  

  downward 
  to 
  the 
  primary 
  lamellse 
  of 
  the 
  coil 
  and 
  returning 
  

   meet 
  the 
  lateral 
  branches 
  below 
  their 
  point 
  of 
  union, 
  the 
  whole 
  

   forming 
  a 
  scissors-shaped 
  arrangement 
  essentially 
  like 
  that 
  of 
  

   Meristella, 
  differing 
  only 
  in 
  minor 
  respects 
  indicated 
  under 
  the 
  

   discussion 
  of 
  that 
  genus. 
  

  

  External 
  surface 
  of 
  the 
  valves 
  smooth 
  or 
  with 
  concentric 
  

   growth-lines. 
  Shell-substance 
  fibrous. 
  

  

  Type, 
  Merista 
  herculea, 
  Barrande. 
  Etage 
  E. 
  

  

  Distribution. 
  Upper 
  Silurian. 
  — 
  Devonian. 
  

  

  Dicamara, 
  Hall. 
  1893. 
  

   (Plate 
  33, 
  figs. 
  16-19.) 
  

   Meristoid 
  shells 
  with 
  a 
  " 
  shoe-lifter 
  " 
  in 
  each 
  valve 
  ; 
  that 
  of 
  

   the 
  brachial 
  valve 
  being 
  divided 
  by 
  a 
  vertical 
  median 
  septum. 
  

   Type, 
  Dicamara 
  plebeia, 
  Sowerby 
  (sp.). 
  

   Distribution. 
  Devonian. 
  

  

  24 
  

  

  