﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  

  

  195 
  

  

  Rhynchonella 
  (?) 
  bidentata 
  (HisingerJ 
  (Fig. 
  iii). 
  Atrypa 
  

   bidentat-a 
  Hall 
  (1852. 
  Pal. 
  N. 
  Y. 
  2:276, 
  

  

  pl. 
  57) 
  

  

  Distinguishing 
  characters. 
  Triangular 
  form; 
  

   acute, 
  extended 
  beak 
  of 
  pedicle 
  valve; 
  stronger 
  

   convexity 
  o-f 
  brachial 
  valve; 
  less 
  convex 
  and 
  more 
  

   triangularly 
  acute 
  than 
  preceding; 
  very 
  slight 
  

  

  . 
  ^ 
  , 
  . 
  ^. 
  , 
  „ 
  . 
  . 
  , 
  ,. 
  Fig. 
  m 
  Rhynchcnel- 
  

  

  frontal 
  emarefination 
  ; 
  shallow 
  smus 
  with 
  one 
  ph-ia 
  (?) 
  wdentata 
  with 
  

  

  *^ 
  surface 
  enlarged 
  

  

  cation, 
  and 
  corresponding 
  fold 
  with 
  two. 
  

  

  Found 
  in 
  the 
  Rochester 
  shale 
  at 
  Lockport 
  and 
  elsewhere 
  (Hall). 
  

   Probably 
  also 
  at 
  Niagara. 
  

  

  Genus 
  atrypa 
  Dalman 
  

  

  [Ety.: 
  a, 
  without; 
  rpu-a, 
  foramen 
  (erroneous)] 
  

  

  (1828. 
  Kongl. 
  Vetenskaps 
  Akad. 
  Handlingar, 
  p. 
  127; 
  1894. 
  Pal. 
  

  

  N. 
  Y. 
  V. 
  8, 
  pt 
  2, 
  p. 
  163) 
  

  

  Shell 
  varying 
  in 
  outline 
  from 
  nearly 
  circular 
  to 
  longitudinally 
  

   suboval; 
  valves 
  very 
  unequal, 
  brachial 
  valve 
  being 
  strongly 
  convex 
  

   or 
  gibbous, 
  while 
  the 
  pedicle 
  valve 
  is 
  gently 
  convex 
  or 
  almost 
  flat 
  

   or 
  sometimes 
  slightly 
  concave 
  from 
  the 
  strongly 
  marked 
  sinus; 
  

   beak 
  of 
  the 
  pedicle 
  valve 
  small 
  and 
  incurved 
  over 
  that 
  of 
  the 
  

   brachial. 
  Large 
  widely 
  separated 
  and 
  doubly 
  grooved 
  teeth 
  are 
  

   present, 
  unsupported 
  by 
  lamellae. 
  Strong 
  muscular 
  impressions. 
  

   Spirals 
  of 
  the 
  brachidium 
  with 
  their 
  bases 
  parallel 
  to 
  the 
  inner 
  sur- 
  

   face 
  of 
  the 
  pedicle 
  valve, 
  and 
  the 
  apexes 
  directed 
  toward 
  the 
  deepest 
  

   point 
  of 
  the 
  opposite 
  valve. 
  Surface 
  radially 
  plicate. 
  

  

  Atrypa 
  reticularis 
  (Linnaeus) 
  (Fig. 
  112) 
  (1852. 
  Pal. 
  N. 
  Y. 
  

   2:272, 
  pl. 
  23, 
  p. 
  270, 
  pl. 
  55) 
  

  

  Fig. 
  112 
  Atrypa 
  reticularis 
  

  

  Distinguishing 
  characters. 
  Convex 
  brachial 
  and 
  flat 
  pedicle 
  

   valves 
  ; 
  small 
  deeply 
  incurved 
  beaks 
  ; 
  radiating 
  and 
  concentric 
  striae 
  

   forming 
  reticulated 
  surface. 
  

  

  