﻿4B4: 
  Panama 
  Shells. 
  arcid^. 
  

  

  Area 
  mutabilis 
  Orb. 
  Voy. 
  Amer, 
  Merid. 
  Moll. 
  p. 
  638. 
  1846. 
  

  

  Station. 
  — 
  Under 
  stones 
  ; 
  Cuming 
  ! 
  Sowerby 
  : 
  also 
  Reeve. 
  

   Our 
  specimens 
  were 
  found 
  under 
  stones 
  and 
  in 
  the 
  crevices 
  

   of 
  rocks, 
  near 
  low 
  water 
  mark. 
  

  

  Habitat. 
  — 
  I. 
  of 
  Plata; 
  Cuming! 
  Sowerby: 
  also 
  Eeeve: 
  also 
  

   Orbignj. 
  

   West 
  Columbia 
  ; 
  Hanlej. 
  

   I. 
  of 
  Plata 
  ; 
  Jay. 
  

   Panama 
  and 
  Taboga 
  ; 
  C. 
  B, 
  A, 
  ! 
  

   70 
  specimens 
  were 
  collected 
  ; 
  among 
  them 
  are 
  some 
  remark- 
  

   able 
  varieties 
  of 
  form. 
  

  

  419. 
  Area 
  (Byssoarca) 
  plioladiformis. 
  Nov. 
  sp. 
  

  

  Shell 
  extremely 
  elongated, 
  subcylindrical, 
  contracted 
  ante- 
  

   riorly, 
  very 
  inequilateral 
  : 
  inferior 
  margin 
  a 
  little 
  irregular, 
  

   somewhat 
  excurved, 
  scarcely 
  gaping 
  for 
  the 
  passage 
  of 
  the 
  bys- 
  

   sus: 
  posterior 
  margin 
  very 
  oblique, 
  moderately 
  excurved 
  : 
  ante- 
  

   rior 
  margin 
  well 
  rounded 
  : 
  dingy 
  white 
  : 
  surface 
  very 
  finely 
  and 
  

   closely 
  fimbriated, 
  with 
  the 
  concentric 
  ridges 
  larger 
  except 
  above 
  

   the 
  posterior 
  angle 
  of 
  the 
  umbo, 
  on 
  which 
  the 
  concentric 
  ridges 
  

   are 
  lamellar 
  : 
  with 
  the 
  intersections 
  nodular 
  and 
  deeply 
  marked 
  

   beneath 
  with 
  the 
  arcuate 
  strice 
  of 
  growth 
  : 
  umbones 
  flattened, 
  

   with 
  a 
  very 
  prominent 
  and 
  very 
  oblique 
  posterior 
  angle, 
  from 
  

   which 
  the 
  radiating 
  ribs 
  divaricate: 
  beaks 
  small: 
  area 
  of 
  

   ligament 
  linear, 
  nearly 
  concealed 
  : 
  margins 
  of 
  the 
  interior 
  finely 
  

   crenulate 
  ; 
  teeth 
  obsolete 
  at 
  the 
  middle 
  of 
  the 
  series, 
  at 
  the 
  

   ends 
  divaricate. 
  The 
  sculpture 
  is 
  like 
  that 
  of 
  A. 
  divaricata 
  

   Reeve. 
  

  

  Length 
  1.25 
  inch 
  ; 
  height 
  .53 
  inch 
  ; 
  breadth 
  .48 
  inch. 
  

  

  Station. 
  — 
  In 
  soft 
  stones, 
  near 
  low 
  water 
  mark. 
  

  

  ^aJzto^.— 
  Taboga; 
  C. 
  B. 
  A. 
  ! 
  

  

  2 
  specimens 
  of 
  this 
  extraordinary 
  shell 
  were 
  obtained. 
  

  

  