﻿952 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  Aperturati 
  ; 
  their 
  surface 
  is 
  frequently 
  ornamented 
  with 
  fine 
  

   granules 
  or 
  interrupted 
  radiating 
  strise. 
  The 
  cardinal 
  process 
  is 
  

   developed 
  as 
  a 
  broad, 
  thin, 
  spreading 
  plate, 
  crossed 
  longitudin- 
  

   ally 
  by 
  numerous 
  linear 
  depressions. 
  A 
  feature 
  which 
  appears 
  

   at 
  times 
  in 
  other 
  groups, 
  but 
  which 
  here 
  possesses 
  the 
  highest 
  

   significance, 
  is 
  the 
  gradual 
  development 
  of 
  the 
  callosity 
  or 
  trans- 
  

   verse 
  plate 
  in 
  the 
  apex 
  of 
  the 
  delthyrium. 
  Originally, 
  and 
  

   always 
  in 
  the 
  earlier 
  species 
  (8.perextensus, 
  Meek 
  and 
  Worthen, 
  

   8. 
  macrotkyris, 
  Hall, 
  etc.), 
  an 
  accompaniment 
  of 
  adult 
  or 
  senile 
  

   growth, 
  it 
  eventually 
  becomes 
  a 
  permanent 
  character 
  existing 
  

   throughout 
  all 
  the 
  later 
  immature 
  growth-phases 
  of 
  the 
  shell. 
  

   In 
  its 
  simpler 
  manifestations 
  it 
  is 
  a 
  testaceous 
  deposit 
  extending 
  

   across 
  the 
  delthyrium 
  from 
  its 
  inner 
  margins; 
  as 
  its 
  size 
  increases 
  

   it 
  unites 
  the 
  dental 
  lamellae, 
  fills 
  the 
  rostral 
  cavity 
  of 
  the 
  valve 
  

   and 
  extends 
  forward 
  along 
  the 
  bottom 
  of 
  the 
  shell 
  between 
  the 
  

   posterior 
  extremities 
  of 
  the 
  diductor 
  muscular 
  bands. 
  This 
  is 
  

   its 
  condition 
  as 
  usually 
  seen 
  in 
  the 
  middle 
  Devonian 
  species, 
  

   8. 
  granulosus 
  and 
  8. 
  audaculus. 
  

  

  Not 
  infrequently 
  this 
  plate 
  is 
  less 
  thickened 
  and 
  extends 
  

   downward 
  with 
  a 
  convex 
  outer 
  surface 
  for 
  two-thirds 
  the 
  length 
  

   of 
  the 
  delthyrium, 
  but 
  this 
  particular 
  form 
  of 
  development 
  

   occurs 
  less 
  often 
  in 
  the 
  early 
  species. 
  

  

  In 
  all 
  its 
  phases 
  it 
  may 
  be 
  coexistent 
  with 
  the 
  true 
  deltidium, 
  

   though 
  the 
  latter 
  is 
  rarely 
  retained 
  in 
  growth-stages 
  where 
  the 
  

   apical 
  callosity 
  is 
  well 
  developed. 
  

  

  Section 
  VI. 
  Glabrati. 
  (Plate 
  29, 
  figs. 
  1-3.) 
  T} 
  T 
  pical 
  examples, 
  

   Spirifer 
  glaber, 
  Martin, 
  Martiniopsis 
  mflata, 
  Waagen. 
  

  

  Forms 
  with 
  the 
  surface 
  smooth 
  and 
  glabrous 
  ; 
  fold 
  and 
  sinus 
  

   faintly 
  developed 
  except 
  at 
  the 
  anterior 
  margins 
  of 
  the 
  

   valves. 
  

  

  The 
  species 
  embraced 
  in 
  this 
  division 
  have 
  stronger 
  differential 
  

  

  characters 
  than 
  are 
  found 
  among 
  the 
  preceding 
  groups. 
  The 
  

  

  shells 
  have 
  a 
  very 
  short 
  hinge 
  and 
  low 
  cardinal 
  area, 
  and 
  the 
  

  

  subcircular 
  marginal 
  outline 
  causes 
  a 
  noticeable 
  alteration 
  in 
  the 
  

  

  orm 
  of 
  the 
  spiral 
  arms. 
  These 
  have 
  their 
  bases 
  well 
  forward 
  

  

  and 
  are 
  extended 
  obliquely 
  to 
  the 
  rounded 
  cardinal 
  extremities, 
  

  

  in 
  their 
  position 
  thus 
  approximating 
  the 
  form 
  assumed 
  by 
  these 
  

  

  organs 
  in 
  Cyrtia 
  and 
  Cyrtina 
  the 
  crura, 
  also, 
  and 
  the 
  primary 
  

  

  lamellae 
  become 
  very 
  long. 
  

  

  10 
  

  

  