﻿808 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  might 
  be 
  conveniently 
  associated 
  on 
  the 
  basis 
  of 
  this 
  feature, 
  it 
  is 
  

   doubtful 
  whether 
  such 
  grouping 
  would 
  be 
  a 
  natural 
  one, 
  or 
  a 
  

   proper 
  expression 
  of 
  the 
  relations 
  of 
  these 
  forms 
  to 
  the 
  various 
  

   contemporary 
  mature 
  types. 
  

  

  In 
  AcROTRETA, 
  CoNOTRETA, 
  LlNNARSSONIA, 
  AcROTHELE 
  and 
  

  

  Iphidea 
  the 
  pedicle 
  aperture 
  is 
  persistently 
  located 
  at 
  the 
  apex 
  of 
  

   the 
  pedicle-valve. 
  This 
  group 
  of 
  genera 
  is 
  one 
  of 
  very 
  early 
  date 
  

   for 
  the 
  most 
  part 
  contemporaneous 
  with 
  Paterina, 
  and 
  the 
  

   existing 
  evidence 
  would 
  indicate 
  that 
  it 
  was 
  not 
  directly 
  ancestral 
  

   to 
  the 
  line 
  of 
  Trematis-Orbiccloidea 
  {Discinidje). 
  The 
  incipient 
  

   formation 
  of 
  an 
  internal 
  foraminal 
  tube 
  is 
  seen 
  in 
  several 
  of 
  these 
  

   genera 
  (Acrotreta, 
  Acrothele, 
  Linnarssonia), 
  and 
  this 
  feature 
  

   attains 
  its 
  maximum 
  in 
  the 
  true 
  Sipbonoireta 
  of 
  the 
  Lower 
  

   Silurian, 
  where 
  the 
  foramen 
  is 
  still 
  apical 
  and 
  the 
  tube 
  wholly 
  

   internal. 
  Hence 
  Siphonoireta 
  appears 
  to 
  be 
  a 
  normal 
  termina- 
  

   tion 
  of 
  this 
  line 
  of 
  descent. 
  Schizambon, 
  in 
  the 
  comprehensive 
  

   meaning 
  of 
  the 
  term 
  ascribed 
  to 
  it 
  in 
  this 
  work, 
  has 
  the 
  pedicle- 
  

   passage 
  superficial, 
  and 
  in 
  such 
  shells 
  as 
  Sckizambon 
  fissus, 
  

   Kutorga, 
  and 
  var. 
  Canadensis, 
  Ami, 
  the 
  condition 
  of 
  this 
  passage 
  

   is 
  perfectly 
  analogous 
  to 
  that 
  of 
  Siphonotre 
  ta, 
  the 
  entire 
  differ- 
  

   ence 
  being 
  in 
  the 
  enclosure 
  of 
  the 
  latter. 
  In 
  Schizambon 
  the 
  

   fibres 
  of 
  the 
  pedicle, 
  extending 
  through 
  the 
  foramen 
  near 
  the 
  

   middle 
  of 
  the 
  pedicle-valve, 
  were 
  directed 
  toward 
  the 
  apex 
  of 
  

   that 
  valve, 
  and 
  along 
  the 
  concave 
  floor 
  of 
  the 
  external 
  pedicle- 
  

   groove. 
  The 
  inner 
  aperture 
  of 
  the 
  pedicle-tube 
  in 
  Siphonotreta, 
  

   corresponds 
  to 
  the 
  " 
  foramen" 
  of 
  ScHizAMeotf, 
  and 
  the 
  outer 
  aper- 
  

   ture, 
  or 
  true 
  foramen 
  of 
  the 
  former 
  to 
  the 
  grooved 
  umbo 
  of 
  the 
  

   pedicle-valve 
  in 
  the 
  latter. 
  Hence 
  in 
  Schizambon, 
  thus 
  considered, 
  

   there 
  is 
  no 
  evidence 
  of 
  a 
  progress 
  of 
  the 
  external 
  aperture, 
  or 
  

   true 
  foramen, 
  anteriorly 
  beyond 
  the 
  apex 
  of 
  the 
  pedicle- 
  valve. 
  

   These 
  two 
  genera 
  are 
  but 
  slight 
  departures 
  from 
  the 
  same 
  type 
  

   of 
  structure, 
  but 
  it 
  would 
  appear 
  that 
  this 
  deviation 
  took 
  place 
  

   during 
  primordial 
  times, 
  as 
  the 
  typical 
  Schizambon 
  (S. 
  typicalis, 
  

   Walcott) 
  is 
  a 
  primordial 
  fossil. 
  The 
  newly 
  described 
  genus 
  

   Trematobolus, 
  Matthew* 
  (T. 
  insignis, 
  Matthew, 
  type), 
  appears 
  

   to 
  be 
  another 
  primordial 
  representative 
  of 
  this 
  structure, 
  

   with 
  the 
  tubular 
  enclosure 
  of 
  the 
  pedicle 
  more 
  highly 
  devel- 
  

  

  * 
  Canadian 
  Record 
  of 
  Science, 
  January, 
  1893, 
  pp. 
  277-279, 
  figs. 
  1 
  a-d. 
  

  

  