﻿Report 
  of 
  the 
  State 
  Geologist. 
  807 
  

  

  on 
  the 
  cardinal 
  edges 
  (Lindstrom) 
  . 
  This 
  mode 
  of 
  articulation 
  

   though 
  not 
  frequently 
  seen 
  in 
  American 
  specimens 
  of 
  Trimerella, 
  

   is 
  so 
  much 
  like 
  that 
  of 
  Eichwaldia, 
  and 
  the 
  general 
  form 
  of 
  the 
  

   shells 
  of 
  the 
  two 
  genera 
  is 
  so 
  similar 
  that 
  there 
  is 
  a 
  good 
  excuse 
  

   for 
  associating 
  them 
  closely, 
  as 
  has 
  been 
  done 
  by 
  (Ehlert, 
  who 
  

   places 
  the 
  latter 
  genus 
  among 
  the 
  Inarticulates. 
  Eichwaldia 
  

   presents 
  a 
  peculiar 
  modification 
  of 
  the 
  pedicle-passage, 
  and 
  all 
  its 
  

   essential 
  characters 
  acquired 
  at 
  an 
  early 
  Silurian 
  age 
  were 
  main- 
  

   tained 
  to 
  the 
  close 
  of 
  the 
  Upper 
  Silurian 
  without 
  substantial 
  

   variation. 
  The 
  origin 
  of 
  Eichwaldia 
  is, 
  at 
  present, 
  but 
  a 
  matter 
  

   of 
  conjecture 
  ; 
  such 
  resemblance 
  as 
  it 
  bears 
  to 
  Trimerella, 
  in 
  its 
  

   incipient 
  articulating 
  apparatus, 
  seems 
  to 
  be 
  only 
  an 
  instance 
  of 
  

   isomorphy. 
  

  

  The 
  second 
  main 
  division 
  of 
  the 
  Inarticulate 
  genera 
  is 
  com- 
  

   posed 
  of 
  those 
  in 
  which 
  the 
  pedicle-aperture, 
  in 
  the 
  immature 
  

   stages 
  or 
  in 
  primitive 
  adult 
  conditions, 
  takes 
  the 
  form 
  of 
  a 
  mar- 
  

   ginal 
  incision 
  of 
  the 
  pedicle-valve, 
  but 
  becomes 
  inclosed 
  in 
  the 
  

   shell-substance 
  in 
  later 
  stages 
  of 
  growth. 
  To 
  this 
  group 
  Waagen 
  

   applied 
  the 
  term 
  Diacaulia* 
  (or 
  Disctnacea, 
  1883), 
  which, 
  like 
  

   Mesocatjlia, 
  is 
  an 
  admirable 
  expression 
  of 
  the 
  significance 
  of 
  the 
  

   pedicle-passage. 
  The 
  name 
  NnofBEMATA 
  was 
  subsequently 
  intro- 
  

   duced 
  by 
  Be 
  c 
  >r 
  (1891) 
  as 
  an 
  ordinal 
  term 
  for 
  not 
  only 
  such 
  

   forms 
  as 
  these, 
  but 
  also 
  for 
  those 
  like 
  Crania 
  of 
  whose 
  fixation 
  

   by 
  means 
  of 
  a 
  pedicle 
  there 
  is 
  yet 
  no 
  evidence. 
  

  

  The 
  mode 
  of 
  development 
  and 
  enclosure 
  of 
  the 
  marginal 
  

   incision 
  in 
  the 
  genus 
  Obbiculoidea 
  has 
  already 
  been 
  demon- 
  

   strated^ 
  and 
  it 
  has 
  been 
  shown 
  that 
  (Ehlerteli 
  a, 
  Trematis 
  and 
  

   Schizocrania 
  which 
  have 
  an 
  unenclosed 
  aperture 
  at 
  maturity, 
  are 
  

   primitive 
  conditions 
  through 
  which 
  Orbici 
  loidea 
  passes 
  in 
  the 
  

   development 
  of 
  the 
  individual 
  . 
  These 
  primitive 
  adult 
  conditions 
  

   occur 
  in 
  various 
  faunas 
  from 
  the 
  primordial 
  (Discinolepis) 
  to 
  

   the 
  Lower 
  Carboniferous 
  (GEhler^ella), 
  and 
  while 
  these 
  genera 
  

  

  * 
  This 
  name 
  was 
  originally 
  printed 
  Daikaulia, 
  probably 
  a 
  typographical 
  error 
  in 
  the 
  spelling 
  

   of 
  the 
  first 
  syllabi 
  -s. 
  

  

  Waagen. 
  following 
  usage 
  in 
  the 
  employment 
  of 
  the 
  terms 
  Lyopomata 
  and 
  Arthropomata, 
  as 
  

   ordinal 
  designations, 
  subordinate 
  ODly 
  to 
  the 
  name 
  of 
  the 
  Class, 
  Prachiopoda. 
  introduce 
  Meso- 
  

   catjlia 
  and 
  Diacauxta 
  as 
  names 
  of 
  Suborders 
  It 
  is 
  a 
  purely 
  arbitrary 
  matter 
  whether 
  the 
  

   former 
  terms 
  be 
  regarded 
  as 
  designations 
  of 
  orders 
  or 
  subclasses. 
  They 
  are, 
  in 
  en 
  her 
  case, 
  

   inferior 
  in 
  the 
  first 
  degree 
  to 
  the 
  Class 
  itself. 
  Hence 
  the 
  fact 
  that 
  Waagen 
  employed 
  i 
  he 
  latter 
  

   terms 
  as 
  suborders 
  Is 
  no 
  ground 
  for 
  rejecting 
  either 
  of 
  them 
  for 
  a 
  later 
  name, 
  but 
  having 
  the 
  

   same 
  breadth 
  of 
  meaning. 
  

  

  t 
  Volume 
  VHI, 
  Part 
  I, 
  loc. 
  cit. 
  

  

  