﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  209 
  

  

  Found 
  in 
  a 
  loose 
  block 
  of 
  limestone, 
  probably 
  the 
  lower 
  Lock- 
  

   port 
  limestone, 
  at 
  Niagara. 
  One 
  specimen. 
  

  

  The 
  identification 
  with 
  Hall's 
  species 
  and 
  the 
  generic 
  reference 
  

   are 
  provisional. 
  

  

  Genus 
  MODioLOPSisHall 
  

  

  [Ety. 
  : 
  Modiolus, 
  a 
  genus 
  of 
  recent 
  shells; 
  d^f?, 
  appear- 
  

   ance 
  (similar 
  to)] 
  

  

  (1847. 
  Pal 
  N. 
  Y. 
  1:157) 
  

  

  Shells 
  equivalve; 
  valves 
  elongate 
  oval, 
  closed, 
  with 
  nearly 
  ter- 
  

   minal 
  beaks 
  and 
  narrow 
  hinge 
  plate, 
  and 
  without 
  teeth; 
  adductor 
  

   scars 
  subequal; 
  ligament 
  deep-seated. 
  

  

  Modiolopsis 
  orthonota 
  (Conrad) 
  (Fig. 
  137) 
  (Hall. 
  1852. 
  Pal 
  

   N. 
  Y. 
  2:10, 
  pi. 
  4 
  bis) 
  

  

  Distinguishing 
  characters. 
  Subelliptic 
  or 
  

   rhomboidal 
  form; 
  straight 
  hinge 
  line; 
  obliquely 
  

   truncated 
  anterior 
  and 
  rounded 
  posterior 
  ends; 
  

   ventral 
  and 
  dorsal 
  margins 
  nearly 
  parallel; 
  ele- 
  

   vated, 
  thin, 
  sharp 
  umbones, 
  with 
  a 
  faint 
  ridge 
  

   extending 
  to 
  the 
  posterior 
  basal 
  margin; 
  sur- 
  Fig. 
  137 
  Modioiopsis 
  onuo 
  

   face 
  with 
  concentric 
  growth 
  lines 
  only. 
  

  

  Found 
  in 
  the 
  upper 
  Medina 
  sandstones 
  at 
  Niagara. 
  Also 
  in 
  the 
  

   same 
  beds 
  at 
  Lockport, 
  usually 
  as 
  molds. 
  

  

  Modiolopsis 
  primigenia 
  (Conrad) 
  (Fig. 
  138) 
  (Hall. 
  1852. 
  Pal. 
  

   N. 
  Y. 
  2:10, 
  pi. 
  4 
  bis) 
  

  

  Distinguishing 
  characters. 
  Subrhomboidal 
  form 
  ; 
  rounded 
  anterior 
  

   and 
  expanded 
  alate 
  posterior 
  ends; 
  straight 
  

   hinge 
  line, 
  produced 
  posteriorly; 
  rounded 
  ven- 
  

   tral 
  margin; 
  fine 
  radiating 
  striae 
  visible 
  only 
  

   in 
  well 
  preserved 
  shells; 
  strong 
  concentric 
  

  

  ^Fi«. 
  138 
  Modiolopsis 
  prim:- 
  g^OWth 
  liuCS. 
  

  

  Found 
  usually 
  as 
  internal 
  molds, 
  in 
  the 
  upper 
  

   Medina 
  sandstones 
  of 
  the 
  Niagara 
  sections, 
  and 
  at 
  Lockport 
  and 
  

   elsewhere. 
  

  

  Modiolopsis 
  sp. 
  (Compare 
  M. 
  subalatus. 
  Pal. 
  N. 
  Y. 
  2:84, 
  

   pi. 
  27, 
  fig. 
  5, 
  6; 
  p. 
  285, 
  pi. 
  59, 
  fig. 
  7) 
  

  

  Distinguishing 
  characters. 
  A 
  small 
  left 
  valve, 
  strongly 
  convex 
  

   below 
  the 
  umbo; 
  a 
  strong 
  cardinal 
  ridge 
  extends 
  from 
  beak 
  to 
  pos- 
  

  

  