﻿The 
  Fauna 
  of 
  the 
  Niagara 
  Group. 
  159 
  

  

  MERISTELLA 
  Hall. 
  

  

  Subgenus 
  MERISTINA 
  Hall. 
  

   Meristhsta 
  Maria. 
  

  

  Plate 
  25, 
  Figs. 
  8-12. 
  

  

  Meristella 
  Maria 
  Hall.. 
  Trans. 
  Alb. 
  Inst., 
  vol. 
  iv, 
  p. 
  212. 
  Abstract 
  p. 
  18; 
  May, 
  

  

  1863. 
  

   Meristina 
  Maria 
  Hall. 
  Pal. 
  N. 
  Y., 
  vol. 
  iv, 
  p. 
  299. 
  1867. 
  

  

  Shell 
  of 
  medium 
  or 
  large 
  size, 
  ventricose, 
  broadly 
  ovate 
  or 
  

   subquadrangular. 
  Ventral 
  valve 
  gibbous 
  above, 
  with 
  a 
  sub- 
  

   angular 
  ridge 
  extending 
  from 
  the 
  beak 
  to 
  near 
  the 
  middle, 
  

   where 
  it 
  becomes 
  flattened, 
  sinuate 
  and 
  bent 
  abruptly 
  up- 
  

   ward 
  in 
  a 
  prolonged 
  linguiform 
  extension 
  ; 
  beak 
  obtuse, 
  

   closely 
  incurved 
  over 
  the 
  opposite 
  valve 
  ; 
  cardinal 
  slopes 
  an- 
  

   gular 
  and 
  the 
  cardinal 
  border 
  inflected. 
  Dorsal 
  valve 
  gibbous, 
  

   strongly 
  arcuate 
  transversely, 
  prominently 
  subangular 
  along 
  

   the 
  middle, 
  and 
  in 
  the 
  lower 
  part 
  presenting 
  a 
  broad 
  undefined 
  

   fold, 
  deeply 
  emarginate 
  in 
  front 
  for 
  the 
  reception 
  of 
  the 
  exten- 
  

   sion 
  of 
  the 
  opposite 
  valve 
  ; 
  beak 
  obtuse, 
  strongly 
  incurved. 
  

  

  Surface 
  marked 
  by 
  strong 
  concentric 
  lines 
  of 
  growth. 
  In- 
  

   terior 
  of 
  ventral 
  valve 
  marked 
  by 
  two 
  strong 
  diverging 
  dental 
  

   lamellae 
  which 
  extend 
  to 
  near 
  the 
  middle, 
  limiting 
  a 
  deep 
  tri- 
  

   angular 
  muscular 
  cavity. 
  

  

  This 
  species 
  is 
  most 
  nearly 
  related 
  to 
  Meristella 
  (Merista) 
  

   tumida 
  of 
  European 
  authors, 
  but 
  is 
  less 
  rotund, 
  while 
  that 
  

   species 
  does 
  not 
  possess 
  the 
  peculiar 
  flattening 
  of 
  the 
  cardinal 
  

   half 
  of 
  the 
  ventral 
  valve 
  and 
  its 
  accompanying 
  subangular 
  

   ridge. 
  It 
  diners 
  from 
  all 
  the 
  other 
  species 
  of 
  the 
  Niagara 
  

   and 
  lower 
  Helderberg 
  groups, 
  but 
  approaches 
  in 
  some 
  char- 
  

   acters 
  to 
  the 
  Meristella 
  (Atrypa) 
  crassirostra 
  of 
  the 
  Niagara 
  

   group 
  (Pal. 
  N. 
  Y. 
  vol. 
  ii). 
  The 
  M. 
  nitida 
  occurs 
  with 
  this 
  

   species, 
  and 
  is 
  readily 
  distinguished 
  from 
  it 
  by 
  its 
  emarginate 
  

   front, 
  and 
  the 
  absence 
  of 
  an 
  elevated 
  fold 
  on 
  the 
  dorsal 
  valve. 
  

  

  Very 
  abundant 
  at 
  the 
  Waldron 
  locality. 
  

  

  