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  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  io3 
  

  

  spiral 
  row 
  on 
  the 
  periphery 
  of 
  the 
  whorl 
  are 
  always 
  lined 
  up 
  under 
  

   one 
  another 
  in 
  N. 
  tuberculata, 
  while 
  in 
  E. 
  nodulosus 
  they 
  are 
  not, 
  

   since 
  the 
  upper 
  row 
  bears 
  fewer 
  (and 
  larger) 
  nodules 
  than 
  the 
  lower 
  

   row. 
  

  

  Sexual 
  dimorphism 
  in 
  the 
  form 
  of 
  shell 
  length 
  was 
  very 
  slight 
  in 
  

   103 
  specimens 
  examined 
  from 
  Rincon 
  Lighthouse, 
  Puerto 
  Rico. 
  Of 
  

   that 
  number, 
  38 
  percent 
  were 
  males; 
  their 
  mean 
  shell 
  length 
  was 
  7.7 
  

   mm. 
  The 
  mean 
  length 
  of 
  the 
  females 
  was 
  9.1 
  mm. 
  In 
  Echininus 
  

   the 
  difference 
  in 
  the 
  sizes 
  of 
  the 
  shells 
  of 
  the 
  two 
  sexes 
  was 
  more 
  

   pronounced, 
  but 
  this 
  is 
  a 
  feature 
  which 
  is 
  variable 
  from 
  colony 
  to 
  

   colony 
  in 
  the 
  same 
  species 
  (see 
  Abbott, 
  1949). 
  

  

  Animal. 
  — 
  Live 
  specimens 
  from 
  Rincon 
  Lighthouse, 
  western 
  Puerto 
  

   Rico, 
  were 
  examined. 
  The 
  animal 
  is 
  typically 
  littorinid. 
  The 
  

   tentacles 
  are 
  translucent 
  yellowish 
  with 
  a 
  small, 
  circular 
  band 
  or 
  

   ring 
  of 
  black 
  around 
  the 
  region 
  near 
  the 
  distal 
  end. 
  The 
  underside 
  

   of 
  the 
  foot 
  is 
  yellowish 
  to 
  yellowish 
  gray 
  with 
  a 
  distinct, 
  longitudinal, 
  

   indented 
  line 
  dividing 
  the 
  foot 
  into 
  two 
  lateral 
  areas. 
  The 
  furrow 
  is 
  

   more 
  prominent 
  near 
  the 
  center, 
  and 
  disappears 
  towards 
  the 
  posterior 
  

   and 
  anterior 
  ends 
  of 
  the 
  sole. 
  The 
  waves 
  of 
  progression 
  are 
  retrograde 
  

   and 
  ditaxic 
  (see 
  Vies, 
  1907, 
  and 
  remarks 
  under 
  Tectarius 
  muricatus). 
  

   The 
  foot 
  progresses 
  somewhat 
  in 
  the 
  manner 
  of 
  a 
  person 
  slowly 
  shuf- 
  

   fling 
  forward 
  in 
  a 
  potato 
  sack. 
  

  

  The 
  penis 
  is 
  large 
  and 
  located 
  on 
  the 
  right 
  side 
  of 
  the 
  body 
  under 
  

   the 
  base 
  of 
  the 
  right 
  tentacle. 
  On 
  the 
  anterior 
  edge 
  of 
  the 
  penis 
  

   there 
  is 
  a 
  large, 
  bean-shaped, 
  snow-white 
  gland, 
  and 
  just 
  distal 
  to 
  it 
  

   is 
  a 
  short, 
  fairly 
  large, 
  clear 
  accessory 
  flagellum. 
  The 
  main 
  prong 
  

   of 
  the 
  penis 
  is 
  slender 
  and 
  tapering 
  to 
  a 
  point, 
  with 
  a 
  nearly 
  closed 
  

   seminal 
  groove 
  along 
  the 
  posterior 
  edge. 
  The 
  penis 
  of 
  N. 
  tuberculata 
  

   is 
  very 
  similar 
  to 
  that 
  of 
  preserved 
  specimens 
  I 
  have 
  examined 
  in 
  

   Littorina 
  (Melarhaphe) 
  ziczac 
  Gmelin 
  from 
  the 
  Bahamas. 
  

  

  Radula. 
  — 
  The 
  ribbon 
  is 
  very 
  long 
  with 
  the 
  unused 
  part 
  coiled 
  up 
  

   like 
  a 
  watch 
  spring 
  in 
  a 
  pocket 
  in 
  the 
  dorsal 
  region 
  behind 
  the 
  head. 
  

   One 
  specimen 
  from 
  Puerto 
  Rico 
  had 
  about 
  1,125 
  transverse 
  rows. 
  

   The 
  ribbon 
  is 
  delicate 
  and 
  half 
  as 
  wide 
  as 
  that 
  found 
  in 
  Echininus. 
  

   The 
  central 
  tooth 
  is 
  narrow, 
  with 
  the 
  appearance 
  of 
  having 
  been 
  

   laterally 
  compressed. 
  It 
  bears 
  a 
  large 
  central 
  cusp, 
  and, 
  crowded 
  

   over 
  this, 
  are 
  the 
  two 
  lateral 
  cusps. 
  The 
  lateral 
  and 
  inner 
  marginal 
  

   teeth 
  are 
  massive, 
  each 
  with 
  a 
  large 
  inner 
  cusp 
  and 
  a 
  much 
  smaller 
  

   outer 
  cusp. 
  The 
  outer 
  marginal 
  tooth 
  is 
  smaller, 
  fairly 
  weak; 
  it 
  

   bears 
  5 
  denticles 
  in 
  Puerto 
  Rico 
  specimens 
  and 
  8 
  denticles 
  in 
  Habana, 
  

   Cuba, 
  specimens. 
  

  

  Parasitology. 
  — 
  In 
  living 
  specimens 
  examined 
  from 
  the 
  rocky 
  shore 
  

   near 
  Habana, 
  Cuba, 
  several 
  specimens 
  of 
  N. 
  tuberculata 
  were 
  found 
  to 
  

   be 
  heavily 
  infected 
  with 
  single-tailed, 
  two-eye-spotted 
  cercariae 
  whose 
  

  

  