﻿[Extract 
  from 
  Palaeontology 
  of 
  New 
  York, 
  Vol. 
  VIII, 
  Part 
  2.] 
  

  

  The 
  Evolution 
  of 
  the 
  Genera 
  of 
  the 
  Palaeozoic 
  

  

  Brachiopoda. 
  

  

  SUMMARY. 
  

  

  At 
  the 
  conclusion 
  of 
  the 
  discussions 
  upon 
  the 
  Inarticulate 
  

   palaeozoic 
  genera, 
  some 
  inferences 
  were 
  drawn 
  as 
  to 
  the 
  phylogeny 
  

   and 
  derivation 
  of 
  the 
  more 
  conspicuous 
  types 
  of 
  inarticulate 
  

   structure 
  (Part 
  I, 
  pp. 
  161-170). 
  At 
  that 
  time 
  it 
  had 
  become 
  

   evident 
  that 
  the 
  variation 
  in 
  the 
  form, 
  position 
  and 
  mode 
  of 
  

   enclosure 
  of 
  the 
  pedicle-passage 
  affords, 
  a 
  more 
  satisfactory 
  

   index 
  of 
  lines 
  of 
  progress 
  and 
  development, 
  and 
  gives 
  a 
  more 
  

   lucid 
  and 
  reliable 
  conception 
  of 
  the 
  rise 
  and 
  decline 
  of 
  brachiopod 
  

   genera, 
  than 
  the 
  modifications 
  in 
  any 
  other 
  single 
  character 
  or 
  

   association 
  of 
  characters. 
  

  

  Previous 
  writers 
  have 
  usually 
  ascribed 
  a 
  high 
  value 
  to 
  the 
  dis- 
  

   position 
  of 
  the 
  muscular 
  scars 
  upon 
  the 
  inner 
  surface 
  of 
  the 
  

   valves, 
  the 
  form 
  of 
  the 
  geni 
  to 
  -vascular 
  sinuses, 
  the 
  configuration 
  

   and 
  degree 
  of 
  calcification 
  of 
  the 
  brachia. 
  The 
  last 
  of 
  these 
  must 
  

   still 
  be 
  regarded 
  as 
  having 
  a 
  significance 
  inferior 
  in 
  importance 
  

   only 
  to 
  the 
  mode 
  of 
  enclosure 
  of 
  the 
  pedicle 
  ; 
  but 
  to 
  the 
  other 
  

   features 
  mentioned 
  our 
  present 
  knowledge 
  accords 
  a 
  less 
  value 
  

   in 
  classification. 
  By 
  this 
  is 
  meant 
  that 
  the 
  muscular 
  system, 
  

   the 
  disposition 
  and 
  interrelations 
  of 
  the 
  separate 
  muscular 
  bands, 
  

   adheres 
  closely 
  to 
  a 
  standard 
  type 
  of 
  expression 
  throughout 
  the 
  

   Class. 
  

  

  This 
  is 
  especially 
  true 
  of 
  the 
  Articulate 
  genera, 
  where, 
  from 
  

   beginning 
  to 
  end, 
  no 
  radical 
  modification 
  of 
  the 
  type, 
  in 
  this 
  

   respect, 
  is 
  effected. 
  It 
  is 
  less 
  true, 
  perhaps, 
  in 
  the 
  more 
  highly 
  

   specialized 
  and 
  more 
  complicated 
  muscular 
  structures 
  of 
  the 
  

   Inarticulates, 
  a 
  group 
  in 
  which 
  our 
  knowledge 
  of 
  the 
  fossil 
  repre- 
  

   sentatives 
  is 
  not 
  altogether 
  satisfactory 
  on 
  account 
  of 
  the 
  tenuity 
  

  

  