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  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Genus 
  leptaena 
  Dalman 
  

  

  [Ety. 
  : 
  XsTTTo^, 
  thin] 
  

  

  (1828. 
  KongL 
  Svenska 
  Vet. 
  Akad. 
  Handl. 
  p. 
  93,94) 
  

  

  Shells 
  concavo-convex; 
  surface 
  covered 
  by 
  conspicuous 
  concen- 
  

   tric 
  corrugations 
  or 
  wrinkles 
  over 
  the 
  flatter 
  portions 
  of 
  the 
  valves. 
  

   Where 
  these 
  cease, 
  the 
  surface 
  is 
  more 
  or 
  less 
  abruptly 
  deflected, 
  

   forming 
  a 
  conspicuous 
  anterior 
  slope. 
  Whole 
  exterior 
  covered 
  with 
  

   fine, 
  radiating, 
  tubular 
  striae, 
  which 
  in 
  well 
  preserved 
  specimens 
  are 
  

   crenulated 
  by 
  finer 
  concentric 
  striae. 
  Hinge 
  line 
  straight; 
  cardinal 
  

   area 
  narrow. 
  A 
  convex 
  deltidium 
  present, 
  perforated 
  at 
  the 
  apex 
  

  

  by 
  a 
  foramen, 
  which 
  often 
  en- 
  

   croaches 
  on 
  the 
  apex 
  of 
  the 
  valve. 
  

   A 
  trilobed 
  cardinal 
  process 
  and 
  

   well 
  defined 
  muscular 
  impressions 
  

   are 
  present. 
  

  

  Leptaena 
  rhomboidalis 
  (Wah- 
  

  

  lenberg) 
  (Fig. 
  84). 
  Leptaena 
  

   depressa 
  Hall 
  (1852. 
  Pai 
  

   N. 
  Y. 
  2:257, 
  pi. 
  53, 
  fig. 
  6a-l) 
  

   Distinguishing 
  characters. 
  Cor- 
  

  

  Fi^^ 
  84 
  Leptaena 
  rhomboidalis 
  rugatcd 
  part 
  gently 
  COUVCX 
  tO 
  

  

  slightly 
  concave; 
  abrupt 
  anterior 
  deflection; 
  strong 
  concentric 
  cor- 
  

   rugations 
  and 
  fine 
  striae. 
  Narrow 
  hinge 
  area. 
  

  

  Found 
  in 
  the 
  upper 
  Clinton 
  limestone, 
  the 
  Clinton 
  lenses, 
  and 
  

   the 
  lower 
  Rochester 
  shale 
  up 
  to 
  and 
  in 
  the 
  BryOzoa 
  bed. 
  Rarely 
  

   above 
  this. 
  Also 
  at 
  Lockport 
  and 
  elsewhere 
  (Hall). 
  

  

  Genus 
  stropheodonta 
  Hall 
  

   [Ety.: 
  arpoipri, 
  bend; 
  odoo?, 
  tooth] 
  

  

  (1852. 
  Pal. 
  N. 
  Y. 
  2:63. 
  Hall 
  & 
  Clarke, 
  1892; 
  Pal. 
  N. 
  Y. 
  v. 
  8, 
  

   pt 
  I, 
  p. 
  284) 
  

  

  Shell 
  normally 
  concavo-convex 
  ; 
  hinge 
  line 
  usually 
  equal 
  to 
  or 
  

   greater 
  than 
  the 
  greatest 
  width 
  of 
  the 
  shell. 
  Area 
  of 
  the 
  pedicle 
  

   valve 
  higher 
  than 
  that 
  of 
  the 
  brachial 
  valve, 
  both 
  furnished 
  witli 
  

   projecting 
  denticulations, 
  which 
  interlock 
  and 
  form 
  articulations. 
  

   Muscular 
  areas 
  well 
  marked 
  and 
  variously 
  bounded. 
  A 
  strongly 
  

   marked 
  bifid 
  cardinal 
  process 
  occurs 
  in 
  the 
  brachial 
  valve. 
  

  

  