﻿AMPHIDESMA. 
  Panama 
  iShells. 
  616 
  

  

  St. 
  Elena 
  ; 
  Jay, 
  

   Panama 
  ; 
  C. 
  B. 
  A. 
  ! 
  

   We 
  found 
  4 
  specimens. 
  

  

  489. 
  Amphidesma 
  striosum. 
  Nov. 
  sp. 
  

  

  Shell 
  elliptical, 
  slightly 
  flexuous, 
  inequilateral 
  ; 
  with 
  the 
  

   posterior 
  dorsal 
  margin 
  slightly 
  excurved, 
  with 
  the 
  anterior 
  

   dorsal 
  margin 
  concave, 
  otherwise 
  with 
  the 
  margins 
  well 
  

   rounded 
  : 
  pale 
  yellowish 
  brown 
  : 
  with 
  numerous 
  fine 
  raised 
  con- 
  

   centric 
  lines, 
  and 
  closely 
  crowded 
  radiating 
  striae, 
  which 
  are 
  

   mostly 
  microscopic 
  : 
  beaks 
  small, 
  approximate 
  : 
  umbones 
  con- 
  

   vex 
  : 
  corselet 
  and 
  lunule 
  not 
  well 
  defined. 
  

  

  Length 
  .78 
  inch 
  ; 
  height 
  .71 
  inch 
  ; 
  breadth 
  .33 
  inch. 
  

  

  Station. 
  — 
  Unknown 
  . 
  

  

  Hahitat. 
  — 
  Panama 
  ; 
  C. 
  B. 
  A. 
  ! 
  

   1 
  specimen 
  was 
  found. 
  

  

  490. 
  Amphidesma 
  tortuosiini. 
  Nov. 
  sp. 
  

  

  Shell 
  compressed, 
  subequilateral, 
  triangular 
  above, 
  orbicular 
  

   below, 
  the 
  slightly 
  excurved 
  posterior 
  dorsal 
  margin 
  and 
  the 
  

   slightly 
  concave 
  anterior 
  dorsal 
  margin 
  meeting 
  at 
  an 
  angle 
  of 
  

   about 
  125°, 
  and 
  the 
  rest 
  of 
  the 
  margins 
  being 
  well 
  rounded 
  ; 
  

   posterior 
  side 
  very 
  flexuous, 
  with 
  a 
  broad 
  deep 
  groove 
  on 
  the 
  

   left 
  valve 
  and 
  a 
  corresponding 
  ridge 
  on 
  the 
  right 
  valve 
  : 
  dingy 
  

   white 
  : 
  with 
  numerous 
  concentric 
  ridges, 
  which 
  are 
  crossed 
  by 
  

   radiating 
  striae 
  that 
  are 
  partly 
  microscopic 
  : 
  beaks 
  very 
  minute, 
  

   approximate 
  : 
  left 
  umbo 
  flat, 
  right 
  one 
  convex 
  : 
  corselet 
  and 
  

   lunule 
  long 
  and 
  narrow, 
  deeply 
  concave. 
  

  

  Length 
  1.25 
  inch; 
  height 
  1.1 
  inch 
  ; 
  breadth 
  .35 
  inch. 
  

  

  Station. 
  — 
  Unknown. 
  

  

  Habitat. 
  — 
  Panama 
  ; 
  C. 
  B. 
  A. 
  ! 
  

   1 
  specimen 
  was 
  obtained. 
  

  

  