﻿1106 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  hinge 
  line 
  and 
  no 
  cardinal 
  area. 
  The 
  pedicle-opening 
  is 
  a 
  broad 
  

   triangular 
  fissure, 
  the 
  valves 
  being 
  in 
  contact 
  behind 
  only 
  at 
  and 
  

   near 
  the 
  cardinal 
  angles. 
  Though 
  ihis 
  shell 
  is 
  from 
  the 
  Lower 
  

   Cambrian 
  faunas 
  there 
  are 
  other 
  brachiopods 
  of 
  obolell 
  >id 
  type 
  

   that 
  are 
  quite 
  as 
  ancient 
  ; 
  still 
  Paterina 
  exemplifies 
  the 
  source 
  

   from 
  which 
  the 
  development 
  of 
  more 
  complicated 
  forms 
  has 
  

   proceeded. 
  

  

  From 
  this 
  simplest 
  of 
  all 
  known 
  (and 
  it 
  might 
  be 
  fair 
  to 
  say, 
  

   all 
  possible) 
  brachiopods, 
  the 
  development 
  and 
  specialization 
  of 
  

   generic 
  characters 
  proceeded 
  in 
  various 
  directions. 
  The 
  orbicu- 
  

   lar 
  form 
  and 
  preponderating 
  chitinous 
  shell- 
  substance 
  form 
  

   essential 
  traits 
  of 
  a 
  considerable 
  group 
  of 
  primeval 
  genera 
  repre- 
  

   sented 
  by 
  Obolus, 
  Obolell 
  a, 
  Elkania, 
  etc., 
  in 
  which, 
  however, 
  

   decided 
  progress 
  is 
  evinced 
  in 
  the 
  rapid 
  specialization 
  of 
  the 
  mus- 
  

   cular 
  apparatus 
  as 
  well 
  as 
  in 
  the 
  restriction 
  of 
  the 
  pedicle-passage 
  

   to 
  a 
  narrow 
  slit. 
  Some 
  closely 
  allied 
  forms 
  with 
  highly 
  chitinous 
  

   shell 
  and 
  obolelloid 
  * 
  muscular 
  scars 
  present 
  an 
  elongate 
  rather 
  

   than 
  subcircular 
  outline, 
  and 
  in 
  this 
  respect 
  indicate 
  a 
  departure 
  

   toward 
  the 
  characteristic 
  linguloid 
  exterior. 
  This 
  is 
  first 
  shown 
  

   by 
  the 
  Cambrian 
  and 
  early 
  Silurian 
  genera 
  Lingulella, 
  Lingct- 
  

   lops 
  and 
  Leptoboltjs. 
  

  

  The 
  true 
  Lingula, 
  with 
  its 
  highly 
  complicated 
  muscular 
  

   apparatus, 
  appears 
  to 
  have 
  become 
  established 
  and 
  static 
  some 
  

   time 
  after 
  the 
  opening 
  of 
  the 
  Silurian 
  (Trenton 
  fauna) 
  and 
  we 
  

   have 
  no 
  reason 
  for 
  believing 
  that 
  the 
  type 
  of 
  structure 
  fixed 
  at 
  

   that 
  remote 
  period 
  differs 
  essentially 
  from 
  the 
  typical 
  Lingulas 
  

   of 
  existing 
  seas. 
  It 
  is 
  not 
  that 
  offshoots 
  and 
  modifications 
  were 
  

   not 
  given 
  off, 
  especially 
  during 
  the 
  early 
  periods 
  of 
  its 
  exist- 
  

   ence, 
  but 
  such 
  lateral 
  departures 
  were 
  short-lived 
  and 
  the 
  old 
  

   firmly 
  established 
  generic 
  type, 
  resistant 
  to 
  variation 
  in 
  physical 
  

   surroundings 
  or 
  adapted 
  to 
  the 
  whole 
  vicissitude 
  of 
  marine 
  con- 
  

   ditions, 
  has 
  perpetuated 
  itself 
  without 
  modification 
  as 
  far 
  as 
  

   indicated 
  by 
  the 
  structure 
  of 
  the 
  shell. 
  

  

  Gtlossina, 
  Dignomia, 
  Barroisella 
  and 
  Tomasina, 
  which 
  repre- 
  

   sent 
  early 
  deviations 
  from 
  Lingo 
  la 
  during 
  the 
  Silurian 
  and 
  

   Devonian 
  periods, 
  embody 
  no 
  substantial 
  variations, 
  though 
  the 
  

   last 
  two 
  demonstrate 
  a 
  gradual 
  assumption 
  of 
  articulating 
  processes. 
  

  

  * 
  Obolella 
  is 
  a 
  more 
  elementary 
  type 
  than 
  Obolus, 
  as 
  is 
  strongly 
  evinced 
  by 
  the 
  character 
  

   of 
  the 
  muscular 
  scars. 
  In 
  Obolus 
  the 
  latter 
  are 
  complicated 
  and 
  approach 
  those 
  of 
  Lingula. 
  

  

  164: 
  

  

  

  