﻿LITTORINA. 
  Panama 
  Shells. 
  395 
  

  

  that 
  the 
  former 
  are 
  the 
  extreme 
  limits 
  of 
  variation 
  rather 
  than, 
  

   distinct 
  types. 
  

  

  Station. 
  — 
  We 
  found 
  this 
  species 
  on 
  ledges 
  and 
  large 
  fragments 
  

   of 
  rocks 
  at 
  or 
  above 
  high 
  water 
  mark. 
  

  

  Hahitat. 
  — 
  Sitcha, 
  Mexico, 
  and 
  San 
  Salvador 
  ; 
  Philippi. 
  

   San 
  Salvador 
  ; 
  Jay. 
  

   Taboga, 
  and 
  Panama 
  ; 
  C. 
  B. 
  A. 
  ! 
  

  

  We 
  collected 
  2400 
  specimens. 
  Dr. 
  Philippi's 
  statement 
  of 
  

   habitat 
  is 
  " 
  Oceanus 
  Pacificus, 
  American! 
  borealem 
  alluens 
  ; 
  

   Sitcha 
  ; 
  ora 
  Eeipublicse 
  Mexico 
  ; 
  S. 
  Salvador 
  in 
  America 
  

   centrali 
  :" 
  Philippi. 
  It 
  is 
  scarcely 
  credible 
  that 
  this 
  species 
  

   should 
  have 
  been 
  found 
  in 
  so 
  high 
  a 
  latitude 
  as 
  Sitcha. 
  No 
  

   original 
  testimony 
  is 
  cited. 
  

  

  Littorina 
  aspera, 
  var., 
  is 
  more 
  slender, 
  and 
  the 
  sculpture 
  is 
  

   reduced 
  to 
  spiral 
  impressed 
  lines. 
  33 
  specimens 
  were 
  collected 
  

   at 
  Panama. 
  

  

  233. 
  liittorina 
  atrata. 
  Nov. 
  sp. 
  

  

  Shell 
  conic 
  when 
  young, 
  subglobular 
  when 
  mature 
  : 
  black, 
  

   sometimes 
  with 
  a 
  few 
  whitish 
  spots 
  on 
  the 
  last 
  whorl 
  : 
  with 
  

   spiral 
  keels 
  varying 
  in 
  size 
  and 
  number; 
  usually 
  a 
  strong 
  

   sharp 
  keel 
  is 
  seen 
  on 
  the 
  periphery 
  of 
  the 
  last 
  whorl 
  and 
  in 
  the 
  

   suture, 
  and 
  another 
  appears 
  on 
  the 
  upper 
  jDart 
  of 
  the 
  whorls, 
  

   with 
  one 
  slightly 
  developed 
  between 
  them 
  ; 
  with 
  two 
  or 
  three 
  

   well 
  developed 
  keels 
  beneath 
  the 
  periphery 
  of 
  the 
  last 
  whorl 
  : 
  

   apex 
  acute 
  : 
  spire 
  small, 
  eroded 
  in 
  full 
  grown 
  shells, 
  with 
  the 
  

   outlines 
  moderately 
  curvilinear 
  : 
  whorls 
  four, 
  a 
  little 
  convex, 
  

   with 
  a 
  well 
  impressed 
  suture; 
  last 
  whorl 
  with 
  an 
  acute 
  

   periphery 
  in 
  the 
  young, 
  rounded 
  in 
  the 
  mature 
  shell 
  : 
  aperture 
  

   broadly 
  ovate 
  : 
  labrum 
  well 
  excurved 
  : 
  umbilicus 
  very 
  small. 
  

   This 
  species 
  is 
  variable 
  in 
  form 
  and 
  in 
  sculpture. 
  

  

  Mean 
  divergence 
  from 
  65° 
  to 
  90° 
  in 
  different 
  stages 
  of 
  

   growth 
  ; 
  length 
  .08 
  inch 
  ; 
  breadth 
  .06 
  inch. 
  

  

  Station. 
  — 
  In 
  or 
  near 
  cavities 
  of 
  rocks 
  between 
  half 
  tide 
  and 
  

   high 
  water 
  levels. 
  

  

  