﻿JUKES-BUOAVNE 
  : 
  OX 
  THE 
  PAMILY 
  rETEICOLIDJE. 
  223 
  

  

  and 
  the 
  orifices 
  of 
  both 
  are 
  fringed 
  with 
  small 
  tentacles. 
  Labial 
  

   appendages 
  rather 
  small, 
  triangular. 
  

  

  Comparing 
  the 
  above 
  description 
  with 
  that 
  of 
  Lnjonkairea 
  it 
  will 
  be 
  

   seen 
  that 
  while 
  the 
  animals 
  agree 
  in 
  the 
  characters 
  of 
  mantle 
  and 
  foot, 
  

   they 
  differ 
  entirely 
  in 
  the 
  siphons, 
  which 
  are 
  free 
  in 
  the 
  one 
  and 
  

   united 
  in 
  the 
  other. 
  

  

  Cooperella. 
  — 
  The 
  animal 
  of 
  this 
  has 
  been 
  described 
  by 
  Dr. 
  Dall 
  in 
  

   the 
  following 
  terms 
  : 
  — 
  " 
  Siphons 
  long, 
  slender, 
  separate, 
  the 
  branchial 
  

   fringed 
  at 
  its 
  orifice 
  ; 
  mantle 
  margins 
  simple, 
  free 
  for 
  about 
  half 
  the 
  

   length 
  of 
  the 
  shell 
  ; 
  gills 
  rather 
  small, 
  free, 
  with 
  direct 
  and 
  reflected 
  

   inner 
  and 
  outer 
  laminae 
  ; 
  palpi 
  very 
  small 
  ; 
  foot 
  compressed 
  quadrate, 
  

   without 
  any 
  byssal 
  groove 
  or 
  obvious 
  gland." 
  

  

  It 
  will 
  be 
  seen 
  that 
  the 
  animal, 
  like 
  the 
  shell, 
  has 
  considerable 
  

   resemblance 
  to 
  Lucinopsis, 
  but 
  that 
  the 
  mantle 
  is 
  much 
  more 
  widely 
  

   open 
  in 
  front. 
  

  

  Claudiconclia. 
  — 
  I 
  have 
  not 
  been 
  able 
  to 
  find 
  any 
  special 
  description 
  

   of 
  the 
  animal 
  of 
  Venerwpis 
  montrosa, 
  and 
  until 
  its 
  characters 
  and 
  habits 
  

   are 
  known, 
  especially 
  whether 
  it 
  is 
  really 
  a 
  rock-borer 
  or 
  not, 
  its 
  

   generic 
  alfinities 
  cannot 
  be 
  determined. 
  

  

  4. 
  Conclusions. 
  

  

  Heviewing 
  the 
  preceding 
  descriptions 
  and 
  observations, 
  I 
  conclude 
  

   that 
  the 
  genus 
  Petricola 
  should 
  be 
  restricted 
  to 
  what 
  may 
  be 
  called 
  

   the 
  two 
  typical 
  sections, 
  i.e. 
  the 
  Naranio 
  of 
  Gray 
  and 
  the 
  Rupellaria 
  

   of 
  Bellevue, 
  with 
  Petricolaria 
  as 
  a 
  sub- 
  genus. 
  

  

  In 
  this 
  genus 
  we 
  have 
  a 
  group 
  of 
  boring 
  molluscs, 
  and 
  

   consequently 
  both 
  animal 
  and 
  shell 
  have 
  been 
  modified 
  in 
  accordance 
  

   with 
  this 
  habit. 
  I 
  have 
  no 
  doubt 
  that 
  the 
  original 
  stock 
  from 
  which 
  

   Petricola 
  sprang 
  was 
  a 
  form 
  which 
  merely 
  burrowed 
  in 
  firm 
  sand 
  or 
  

   stiff 
  mud, 
  in 
  the 
  same 
  manner 
  as 
  Lajonkairea 
  does 
  at 
  the 
  present 
  day. 
  

   When 
  for 
  greater 
  security 
  the 
  ancestral 
  form 
  took 
  to 
  excavating 
  

   harder 
  material, 
  the 
  frontal 
  portion 
  of 
  the 
  mantle 
  would 
  be 
  developed 
  

   to 
  a 
  greater 
  extent, 
  and 
  the 
  enlargement 
  of 
  the 
  anterior 
  portion 
  of 
  the 
  

   shell 
  may 
  be 
  correlated 
  with 
  the 
  enlargement 
  of 
  the 
  mantle 
  tissue. 
  

  

  Lajonkairea 
  seems 
  to 
  stand 
  by 
  itself. 
  It 
  is 
  not 
  a 
  boring 
  mollusc, 
  

   and 
  its 
  usual 
  habitat 
  is 
  believed 
  to 
  be 
  hard 
  sand, 
  but 
  sometimes 
  it 
  

   harbours 
  in 
  the 
  rock-burrows 
  of 
  other 
  molluscs, 
  just 
  as 
  Venerupis 
  

   does. 
  It 
  differs 
  much 
  from 
  Petricola 
  both 
  in 
  shell 
  and 
  in 
  animal. 
  

   The 
  siphons 
  are 
  united 
  to 
  their 
  ends 
  instead 
  of 
  being 
  largely 
  separate 
  

   as 
  in 
  Petricola 
  ; 
  while 
  the 
  shell 
  has 
  a 
  fuller 
  and 
  higher 
  posterior 
  than 
  

   anterior 
  development, 
  and 
  the 
  hinge 
  has 
  more 
  divergent 
  teeth 
  in 
  spite 
  

   of 
  the 
  fact 
  that 
  the 
  shell 
  is 
  shorter. 
  In 
  view 
  of 
  these 
  differences 
  

   I 
  think 
  it 
  should 
  form 
  a 
  distinct 
  genus, 
  separate 
  both 
  from 
  Petricola 
  

   and 
  Lucinopsis. 
  

  

  With 
  regard 
  to 
  Lucinopsis 
  we 
  have 
  seen 
  that 
  its 
  internal 
  characters, 
  

   and 
  especially 
  the 
  hinge, 
  agree 
  closely 
  with 
  those 
  of 
  Petricola. 
  Its 
  

   external 
  shape 
  is, 
  of 
  course, 
  very 
  different, 
  but 
  in 
  this 
  respect 
  it 
  may 
  

   be 
  compared 
  with 
  Bosinia, 
  Cyclina, 
  and 
  Cyclimlla, 
  which 
  are 
  all 
  free 
  

   shells, 
  burrowing 
  in 
  sand, 
  while 
  other 
  members 
  of 
  the 
  Veneridse 
  are 
  

   elongate-oval 
  in 
  shape. 
  

  

  