﻿The 
  Evolution 
  and 
  Classification 
  of 
  the 
  Genera 
  

   of 
  the 
  Brachiopoda. 
  

  

  In 
  the 
  foregoing 
  pages, 
  a 
  consecutive 
  account 
  of 
  the 
  characters 
  

   of 
  the 
  various 
  genera 
  of 
  the 
  Brachiopods 
  has 
  been 
  given, 
  without 
  

   attempting 
  to 
  interrupt 
  it 
  with 
  broader 
  designations 
  and 
  group- 
  

   ings. 
  In 
  a 
  work 
  of 
  this 
  nature, 
  such 
  a 
  consecutive 
  narration 
  of 
  

   the 
  genera 
  is 
  necessary, 
  though 
  wholly 
  conventional 
  and 
  

   unnatural. 
  The 
  development 
  of 
  these 
  animals 
  throughout 
  

   geologic 
  time 
  has 
  not 
  been 
  along 
  an 
  undeviating 
  line, 
  but, 
  on 
  the 
  

   contrary, 
  is 
  a 
  series 
  of 
  departures 
  at 
  different 
  periods 
  in 
  their 
  

   history, 
  from 
  various 
  comprehensive 
  and 
  prolific 
  stocks. 
  The 
  

   courses 
  of 
  their 
  existence 
  can 
  be 
  expressed 
  only 
  by 
  divergent 
  and 
  

   ramifying 
  lines 
  branching 
  off 
  here 
  and 
  there 
  at 
  rapid 
  intervals 
  

   during 
  the 
  vigor 
  of 
  the 
  race, 
  the 
  off-shoots 
  becoming 
  more 
  and 
  

   more 
  unlike 
  as 
  their 
  growth 
  continues, 
  at 
  times 
  terminating 
  

   abruptly 
  as 
  though 
  unfavorable 
  conditions 
  had 
  put 
  a 
  period 
  to 
  

   their 
  existence, 
  but 
  usually 
  in 
  their 
  prolonged 
  existence 
  and 
  

   gradual 
  decline 
  resuming 
  many 
  of 
  their 
  early 
  parental 
  traits. 
  

  

  As 
  a 
  preliminary 
  and 
  general 
  principle, 
  it 
  must 
  first 
  be 
  

   observed 
  that, 
  in 
  the 
  development 
  of 
  any 
  great 
  race 
  of 
  organisms 
  

   (always 
  exemplified 
  by 
  those 
  whose 
  history 
  is 
  known 
  for 
  such 
  

   an 
  illimitable 
  period 
  as 
  the 
  Brachiopoda) 
  the 
  specialization 
  of 
  

   generic 
  characters 
  and 
  the 
  evolution 
  of 
  distinct 
  generic 
  stocks 
  is 
  

   carried 
  on 
  with 
  much 
  greater 
  rapidity 
  during 
  their 
  early 
  

   existence 
  than 
  at 
  any 
  time 
  in 
  their 
  later 
  history. 
  The 
  primitive 
  

   types 
  embody 
  the 
  potentialities 
  of 
  all 
  subsequent 
  expressions 
  

   which 
  the 
  race 
  assumes. 
  

  

  It 
  then 
  becomes 
  a 
  question 
  of 
  elementary 
  importance 
  to 
  ascer- 
  

   tain 
  these 
  primitive 
  generic 
  types 
  and 
  to 
  fix 
  upon 
  the 
  radicle 
  or 
  

   root-stock 
  from 
  which 
  all 
  lines 
  of 
  evolution 
  in 
  this 
  group 
  have 
  

   departed. 
  With 
  our 
  present 
  knowledge, 
  it 
  is 
  believed 
  possible 
  

   to 
  approximate 
  these 
  starting 
  points 
  in 
  the 
  history 
  of 
  the 
  race 
  

   with 
  some 
  degree 
  of 
  accuracy. 
  Before, 
  however, 
  proceeding 
  to 
  

  

  159 
  

  

  