﻿196 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Found 
  in 
  all 
  the 
  beds 
  from 
  the 
  upper 
  Clinton 
  limestones 
  to 
  the 
  

  

  Bryozoa 
  beds. 
  Most 
  abundant 
  in 
  the 
  Clinton. 
  

  

  In 
  the 
  light 
  colored 
  crystalline 
  upper 
  Clinton 
  limestone 
  this 
  

   species 
  is 
  very 
  abundant, 
  but 
  also 
  very 
  variable. 
  Strong 
  robust 
  and 
  

   very 
  rotund 
  specimens 
  occur, 
  with 
  brachial 
  valve 
  excessively 
  bulg- 
  

   ing, 
  and 
  with 
  narrow 
  simple 
  rounded 
  striae, 
  increasing 
  by 
  implan- 
  

   tation, 
  and 
  cancelated 
  by 
  concentric 
  striae 
  of 
  moderate 
  strength, 
  and 
  

   stronger 
  undulations 
  on 
  the 
  mature 
  portions. 
  Other 
  specimens, 
  less 
  

   rotund 
  and 
  with 
  bifurcating 
  striae 
  occur. 
  When 
  bifurcation 
  of 
  

   striae 
  occurs, 
  this 
  is 
  usually 
  found 
  on 
  the 
  pedicle 
  valve, 
  those 
  of 
  the 
  

   brachial 
  valve 
  increasing 
  only 
  by 
  intercalation. 
  The 
  pedicle 
  valve 
  

   usually 
  has 
  a 
  sinus 
  near 
  the 
  front, 
  and 
  the 
  striae 
  and 
  concentric 
  lines 
  

   increase 
  in 
  strength, 
  approaching 
  the 
  characters 
  of 
  the 
  next 
  species. 
  

   In 
  the 
  Clinton 
  lenses 
  this 
  character 
  becomes 
  still 
  more 
  pronounced, 
  

   the 
  shells 
  at 
  the 
  same 
  time 
  decreasing 
  in 
  size 
  and 
  rotundity. 
  In 
  the 
  

   Rochester 
  shales 
  the 
  species 
  is 
  generally 
  much 
  less 
  abundant, 
  A. 
  

   nodostriata 
  being 
  the 
  prominent 
  form. 
  A. 
  reticularis 
  

   is 
  represented 
  by 
  small 
  and 
  generally 
  flattened 
  specimens, 
  in 
  which 
  

   the 
  radiating 
  striae 
  are 
  usually 
  fine, 
  and 
  the 
  concentric 
  striae 
  

  

  lamellose, 
  specially 
  in 
  the 
  adult 
  por- 
  

   tions. 
  Increase 
  of 
  striae 
  occurs 
  by 
  

   / 
  both 
  intercalation 
  and 
  bifurcation, 
  

  

  the 
  former 
  on 
  the 
  brachial, 
  the 
  lat- 
  

   ter 
  on 
  the 
  pedicle 
  valve. 
  In 
  some 
  

   specimens 
  the 
  bifurcation 
  occurs 
  close 
  

   to 
  the 
  beak. 
  

  

  Atrypa 
  nodostriata 
  Hall 
  (Fig. 
  113) 
  

   (1852. 
  Pal 
  N. 
  Y. 
  2:272, 
  pi. 
  56) 
  

  

  Distinguishing 
  characters. 
  Sub- 
  

   equal 
  valves, 
  nearly 
  equally 
  convex 
  in 
  

   young, 
  pedicle 
  valve 
  more 
  convex 
  

   with 
  age; 
  small 
  slightly 
  elevated 
  beak 
  

  

  Fig. 
  113 
  Atrypa 
  nodostriata, 
  with 
  striae 
  

  

  enlarged 
  of 
  pediclc 
  valvc 
  ; 
  mcsial 
  sinus 
  in 
  adult 
  

  

  shells, 
  broad 
  and 
  undefined; 
  strong 
  rounded 
  bifurcating 
  plications; 
  

  

  lamellose 
  growth 
  lines 
  which 
  give 
  nodulose 
  appearance 
  to 
  surface. 
  

   Found 
  in 
  the 
  Clinton 
  lenses, 
  and 
  the 
  lower 
  and 
  middle 
  Rochester 
  

  

  shale 
  at 
  Niagara. 
  Specially 
  abundant 
  in 
  the 
  Bryozoa 
  beds. 
  Also 
  

  

  found 
  at 
  Lockport 
  and 
  elsewhere 
  (Hall). 
  

   Atrypa 
  rugosa 
  Hall 
  (Fig. 
  114) 
  (1852. 
  Pal 
  N. 
  Y. 
  2:271, 
  pi. 
  56) 
  

   Distinguishing 
  characters. 
  Generally 
  smaller 
  than 
  preceding; 
  

  

  equally 
  convex 
  valves 
  in 
  adult, 
  unequal 
  in 
  young, 
  the 
  brachial 
  valve 
  

  

  ^ 
  

  

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