﻿i88 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Pal 
  N. 
  F. 
  V. 
  8, 
  

  

  Genus 
  rhipidomella 
  Oehlert 
  

  

  [Ety.: 
  p~L7zi<$, 
  fan] 
  

  

  (1891. 
  Journal 
  de 
  conchy 
  liologie., 
  p. 
  ^y2; 
  1892. 
  

   pt 
  I, 
  p. 
  209) 
  

  

  Shell 
  almost 
  circular 
  in 
  outline; 
  both 
  valves 
  gently 
  convex; 
  hinge 
  

   area 
  short; 
  slight 
  median 
  depression 
  in 
  each 
  valve. 
  Surface 
  cov- 
  

   ered 
  with 
  fine, 
  rounded, 
  hollow, 
  tubular 
  striae, 
  which 
  frequently 
  open 
  

   on 
  the 
  surface. 
  On 
  the 
  interior 
  of 
  the 
  pedicle 
  valve 
  are 
  two 
  strong 
  

   diverging 
  teeth. 
  Muscular 
  area 
  large, 
  and 
  deeply 
  impressed, 
  con- 
  

   sisting 
  of 
  fluted 
  diductor 
  impressions, 
  inclosing 
  small 
  central 
  ad- 
  

   ductors. 
  The 
  pedicle 
  scar 
  fills 
  the 
  cavity 
  of 
  the 
  beak. 
  The 
  interior 
  

   of 
  the 
  brachial 
  valve 
  shows 
  deep 
  and 
  narrow 
  dental 
  sockets, 
  with 
  

   prominent 
  projecting 
  crural 
  plates. 
  In 
  the 
  center 
  is 
  a 
  strong 
  car- 
  

   dinal 
  process, 
  below 
  which 
  is 
  the 
  indistinct 
  small 
  muscular 
  area. 
  

  

  Rhipidomella 
  hybrida 
  (Sowerby) 
  (Fig. 
  98). 
  O 
  r 
  t 
  h 
  i 
  s 
  h 
  y 
  - 
  

  

  1852. 
  Pal. 
  N. 
  Y. 
  2:2^3, 
  pi. 
  52) 
  

  

  Distinguishing 
  characters. 
  Wider 
  

   than 
  long; 
  nearly 
  equal 
  valves; 
  pedi- 
  

   cle 
  valve 
  with 
  broad, 
  undefined 
  de- 
  

   pression 
  down 
  the 
  center; 
  brachial 
  

   valve 
  uniformly 
  convex, 
  sometimes 
  

   slightly 
  depressed 
  near 
  front; 
  beaks 
  

   nearly 
  equally 
  elevated 
  and 
  scarcely 
  

   incurved; 
  short 
  hinge 
  area; 
  fine 
  bi- 
  

   furcating 
  striae. 
  

  

  Found 
  in 
  the 
  upper 
  part 
  of 
  the 
  lower 
  Rochester 
  shales 
  and 
  in 
  the 
  

   Bryozoa 
  bed 
  as 
  well 
  as 
  rarely 
  in 
  the 
  upper 
  shales. 
  Niagara 
  sec- 
  

   tions. 
  Also 
  at 
  Lockport 
  and 
  elsewhere 
  (Hall). 
  

  

  Rhipidomella 
  circulus 
  Hall 
  (Fig. 
  99). 
  Or 
  this 
  circulus 
  

   Hall 
  (1852. 
  Pal. 
  N. 
  Y. 
  2:56, 
  pi. 
  20) 
  

  

  b 
  r 
  i 
  d 
  a 
  Sowerby 
  (Hall. 
  

  

  Fig. 
  98 
  Rhipidomella 
  hybrida 
  

  

  Fig. 
  99 
  Rhipidomella 
  circulus 
  with 
  enlargement 
  of 
  surface 
  

  

  