﻿1112 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  has 
  been 
  shown 
  that 
  Kutorgina 
  cingulata 
  may 
  retain 
  a 
  pedicle- 
  

   covering 
  or 
  external 
  sheath, 
  in 
  fact 
  a 
  true 
  deltidium 
  bearing 
  an 
  

   apical 
  perforation, 
  like 
  that 
  in 
  Clitambonites. 
  The 
  same 
  charac- 
  

   ter 
  is 
  highly 
  developed 
  or 
  fully 
  retained 
  at 
  maturity 
  in 
  Iphidea. 
  

   This 
  is 
  evidence 
  of 
  the 
  highest 
  moment, 
  and 
  conclusively 
  shows 
  

   the 
  line 
  along 
  which 
  the 
  clitambonitoids 
  and 
  strophomenoids 
  have 
  

   been 
  derived. 
  It 
  is 
  an 
  immediate 
  departure 
  from 
  the 
  primitive 
  

   type 
  of 
  the 
  brachiopod 
  into 
  the 
  articulate 
  subtype. 
  

  

  Passage 
  from 
  the 
  inarticulate 
  to 
  the 
  articulate 
  plan 
  of 
  structure 
  

   was 
  thus 
  effected 
  at 
  a 
  very 
  early 
  period 
  ; 
  indeed, 
  almost 
  at 
  the 
  

   outset 
  of 
  the 
  history 
  of 
  the 
  group. 
  The 
  continuance 
  of 
  the 
  two 
  

   types 
  has 
  since 
  been 
  that 
  of 
  diverging 
  series, 
  constantly 
  widening 
  

   the 
  structural 
  gap 
  between 
  them. 
  We 
  have 
  no 
  irrefragible 
  evi- 
  

   dence 
  that 
  this 
  chasm 
  has 
  been 
  bridged 
  at 
  any 
  other 
  point 
  than 
  

   near 
  its 
  source 
  ; 
  the 
  inclinations 
  from 
  the 
  one 
  type 
  toward 
  the 
  

   other, 
  shown 
  in 
  the 
  articulating 
  processes 
  of 
  Barroisella, 
  Tom- 
  

   asista, 
  etc., 
  represent 
  uncompleted 
  accessory 
  lines 
  of 
  development, 
  

   which 
  were 
  abruptly 
  terminated 
  without 
  accomplishing 
  the 
  full 
  

   transitions. 
  Such 
  forms 
  have 
  left 
  no 
  descendants, 
  so 
  far 
  as 
  

   known. 
  

  

  The 
  most 
  elenfentary 
  structure, 
  then, 
  observable, 
  among 
  the 
  

   Articulate 
  Brachiopods 
  is 
  the 
  combination 
  of 
  the 
  deltidium 
  with 
  

   a 
  distinct 
  pedicle-cavity, 
  whose 
  anterior 
  margins 
  are 
  not 
  free, 
  

   and 
  whose 
  lateral 
  walls 
  or 
  dental 
  lamellae 
  are 
  not 
  highly 
  

   developed; 
  these 
  features 
  being 
  accompanied 
  by 
  gently 
  and 
  

   unequally 
  biconvex 
  valves, 
  well-defined 
  cardinal 
  areas 
  and 
  

   elongate 
  hinge-line 
  ; 
  producing, 
  in 
  effect, 
  a 
  generally 
  orthoid 
  

   expression 
  both 
  of 
  interior 
  and 
  exterior. 
  This 
  is 
  the 
  condition 
  

   of 
  Billingsella 
  of 
  the 
  Cambrian, 
  Orthis 
  loricula 
  and 
  0. 
  deflecta 
  

   of 
  the 
  Trenton 
  group, 
  and 
  Of 
  laurentina 
  of 
  the 
  Hudson 
  Eiver 
  

   fauna, 
  and 
  it 
  is 
  continued 
  without 
  essential 
  modification, 
  except 
  

   in 
  the 
  gradual 
  contraction 
  of 
  the 
  pedicle-cavity 
  and 
  deltidium, 
  

   into 
  Strophomena 
  of 
  the 
  Silurian, 
  its 
  allies 
  and 
  successors, 
  

   Orthothetes 
  of 
  the 
  Devonian, 
  and 
  Derbya 
  of 
  the 
  Carboniferous, 
  

   Hipparionyx, 
  Triplegia, 
  Streptorhynchus, 
  etc., 
  into 
  Lepta^ena, 
  

   Rafinesquina, 
  Stropheodonta, 
  Plectambonites, 
  Chonetes 
  and 
  

   Productus. 
  

  

  The 
  tendency 
  to 
  contract 
  the 
  pedicle-cavity 
  and 
  deltidium 
  

   presents 
  its 
  extreme 
  manifestation 
  in 
  the 
  Devonian 
  forms 
  of 
  

  

  170 
  

  

  