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  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  the 
  production 
  of 
  a 
  wonderful 
  series 
  of 
  modifications 
  whose 
  

   relations 
  it 
  is 
  not 
  necessary 
  to 
  rehearse 
  here. 
  The 
  extreme 
  

   range 
  of 
  these 
  modifications 
  is 
  seen 
  in 
  the 
  simple 
  termination 
  of 
  

   the 
  jugum 
  in 
  Whitfieldella, 
  Rhynchospira, 
  etc., 
  the 
  bifurcate 
  

   extremity 
  in 
  Meristina, 
  Eumetria 
  and 
  Retzia, 
  their 
  terminal 
  

   branches 
  finally 
  becoming 
  coextensive 
  in 
  Kayseria, 
  Diplos- 
  

   pi 
  bella, 
  etc., 
  with 
  the 
  lamellae 
  of 
  the 
  primary 
  spirals 
  and 
  thus 
  

   forming 
  a 
  second 
  pair 
  of 
  spiral 
  cones. 
  This 
  complication 
  of 
  the 
  

   brachidium 
  is 
  effected 
  only 
  late 
  in 
  the 
  history 
  of 
  the 
  various 
  

   groups 
  producing 
  them. 
  Koninokina 
  and 
  Amphiclina 
  are 
  double- 
  

   spiraled 
  convexo-concave 
  shells 
  which 
  are 
  the 
  post-palaeozoic 
  and 
  

   final 
  representatives 
  of 
  Anoplotheca 
  and 
  Ccelospira. 
  Rexidella 
  

   and 
  Diplospirella, 
  of 
  the 
  St. 
  Cassian 
  beds, 
  are 
  double-spiraled 
  

   athyroids 
  ; 
  Kayseria 
  of 
  the 
  middle 
  Devonian, 
  which 
  is 
  the 
  only 
  

   double-spiraled 
  form 
  known 
  in 
  the 
  Palaeozoic, 
  appears 
  to 
  be 
  an 
  

   aberrant 
  and 
  accelerated 
  representative 
  of 
  the 
  stock 
  which 
  

   by 
  more 
  gradual 
  development 
  produced 
  Retzia 
  and 
  Eumetria. 
  

  

  But 
  one 
  large 
  group 
  of 
  spire-bearing 
  shells 
  retains 
  the 
  cardinal 
  

   area, 
  namely, 
  the 
  Spiriferidje, 
  a 
  family 
  with 
  everted 
  spirals, 
  one 
  

   of 
  the 
  earliest 
  to 
  appear 
  and 
  the 
  last 
  to 
  disappear. 
  Its 
  abundant 
  

   representatives 
  possess 
  the 
  longest 
  of 
  spirals 
  and 
  for 
  the 
  most 
  

   part 
  these 
  are 
  greatly 
  extended 
  transversely, 
  held 
  at 
  arm's 
  length 
  

   as 
  it 
  were, 
  unsupported 
  by 
  a 
  connected 
  jugum 
  (except 
  in 
  the 
  

   more 
  sparsely 
  represented 
  genera 
  Cyrtina 
  and 
  Spiriferina), 
  but 
  in 
  

   spite 
  of 
  the 
  delicacy 
  of 
  this 
  structure 
  and 
  its 
  apparent 
  mechanical 
  

   disadvantage 
  in 
  the 
  absence 
  of 
  a 
  continuous 
  jugum, 
  the 
  type 
  of 
  

   structure 
  maintained 
  its 
  own 
  and 
  multiplied 
  in 
  a 
  most 
  remarkable 
  

   manner. 
  

  

  The 
  relations 
  of 
  the 
  brachiopods 
  with 
  spiral 
  bracbidia, 
  or 
  

   Helicopegmata, 
  to 
  the 
  Ancylobrachia, 
  or 
  those 
  shells 
  commonly 
  

   spoken 
  of 
  as 
  the 
  terehratuloids, 
  has 
  been 
  a 
  fruitful 
  subject 
  of 
  

   discussion 
  and 
  given 
  rise 
  to 
  investigations 
  of 
  great 
  astuteness 
  

   and 
  merit. 
  Reference 
  has 
  already 
  been 
  made 
  to 
  the 
  facts 
  estab- 
  

   lished 
  by 
  Beecher 
  and 
  Schuchert 
  from 
  the 
  development 
  of 
  the 
  

   brachidium 
  in 
  Zygospira, 
  which 
  show 
  that 
  this 
  atrypid 
  passes 
  

   through 
  a 
  growth 
  stage 
  in 
  which 
  the 
  brachidium 
  has 
  a 
  simple 
  

   terebratuloid 
  form, 
  similar 
  to 
  that 
  in 
  the 
  mature 
  condition 
  of 
  

   Dielasma 
  ; 
  that 
  the 
  spirals 
  are 
  formed 
  by 
  the 
  continued 
  growth 
  

  

  