﻿J0KES-BROWNE 
  : 
  ON 
  THE 
  FAMILY 
  PETEICOLID^. 
  215 
  

  

  as 
  we 
  have 
  seen 
  (in 
  1854). 
  Fischer 
  in 
  1887 
  placed 
  it 
  as 
  a 
  sub-genus 
  

   of 
  Lucinopsis, 
  but 
  retained 
  that 
  genus 
  in 
  the 
  Veneridae. 
  

  

  On 
  the 
  other 
  hand, 
  Dr. 
  Dall 
  in 
  1900 
  separated 
  it 
  from 
  Lucinopsis, 
  

   and 
  gave 
  the 
  name 
  as 
  one 
  of 
  the 
  synonyms 
  of 
  Petricola, 
  remarking 
  

   that 
  " 
  Lajonlcairea 
  of 
  Deshayes 
  is 
  close 
  to 
  Rupellaria, 
  differing 
  chiefly 
  

   by 
  more 
  regular 
  striation, 
  absence 
  of 
  strong 
  concentric 
  structure, 
  and 
  

   rounded 
  rather 
  than 
  pyriform 
  outline". 
  It 
  seems 
  curious 
  that 
  neither 
  

   Dall 
  nor 
  anyone 
  else 
  should 
  have 
  considered 
  the 
  possibility 
  that 
  

   Lucinopsis 
  might 
  also 
  belong 
  to 
  the 
  Petricolidae. 
  

  

  Determination 
  of 
  Types. 
  — 
  The 
  type 
  of 
  Petricola 
  has 
  been 
  incorrectly 
  

   given 
  as 
  P. 
  litliophaga, 
  because 
  this 
  was 
  the 
  first 
  species 
  cited 
  by 
  

   Lamarck 
  in 
  1801 
  ; 
  ^ 
  but 
  Dr. 
  Dall 
  has 
  pointed 
  out 
  that 
  Lamarck 
  cited 
  

   two 
  species, 
  and 
  consequently 
  did 
  not 
  fix 
  the 
  type 
  ; 
  further, 
  that 
  in 
  

   1802 
  Fleuriau 
  de 
  Bellevue 
  separated 
  the 
  first 
  species 
  under 
  the 
  name 
  

   of 
  Rupellaria. 
  It 
  is 
  clear, 
  therefore, 
  that 
  Lamarck's 
  second 
  species, 
  

   the 
  Venus 
  lapicida 
  of 
  Chemnitz, 
  is 
  left 
  to 
  form 
  the 
  type 
  of 
  his 
  genus 
  

   Petricola. 
  As 
  this 
  was 
  also 
  the 
  type 
  of 
  Gray's 
  Naratiio, 
  that 
  name 
  

   consequently 
  becomes 
  a 
  synonym 
  of 
  Petricola. 
  

  

  The 
  type 
  of 
  Choristodon 
  (Jonas, 
  1844) 
  is 
  Ch. 
  typicum, 
  Jonas, 
  and, 
  

   in 
  Dr. 
  Dall's 
  opinion, 
  the 
  characters 
  on 
  which 
  it 
  was 
  based 
  are 
  merely 
  

   pathological. 
  The 
  left 
  anterior 
  and 
  the 
  right 
  posterior 
  teeth 
  are 
  

   generally 
  separated 
  from 
  their 
  bases 
  by 
  a 
  layer 
  of 
  cartilage, 
  but 
  

   Dr. 
  Dall 
  thinks 
  this 
  is 
  due 
  to 
  fracture 
  consequent 
  on 
  the 
  teeth 
  having 
  

   a 
  narrow 
  base. 
  He 
  has 
  found 
  from 
  an 
  examination 
  of 
  a 
  series 
  of 
  

   specimens 
  that 
  sometimes 
  the 
  teeth 
  are 
  only 
  cracked, 
  and 
  that 
  

   occasionally 
  they 
  are 
  perfect. 
  In 
  all 
  other 
  respects 
  the 
  shell 
  is 
  

   similar 
  to 
  that 
  of 
  P. 
  lithophaga, 
  and 
  therefore 
  I 
  agree 
  with 
  Dr. 
  Dall 
  

   that 
  Choristodo7i 
  must 
  rank 
  as 
  a 
  synonym 
  of 
  the 
  Rupellaria 
  section 
  

   of 
  Petricola. 
  

  

  The 
  type 
  Lajonhairea 
  is 
  the 
  Venerupis 
  Lajonhairii 
  of 
  Payraudeau 
  

   (1826), 
  which 
  Philippi 
  afterwards 
  described 
  as 
  V. 
  decussata 
  (1836). 
  

   When 
  Deshayes 
  instituted 
  the 
  genus 
  Lajonhairea 
  he 
  thought 
  himself 
  

   at 
  liberty 
  to 
  adopt 
  Philippi's 
  specific 
  name 
  instead 
  of 
  duplicating 
  the 
  

   generic 
  appellation, 
  but 
  this 
  is 
  not 
  allowed 
  by 
  the 
  rules 
  of 
  the 
  

   Zoological 
  Congress. 
  

  

  The 
  type 
  of 
  Petricolaria 
  is 
  P. 
  pholadiformis, 
  Lam. 
  This 
  was 
  

   proposed 
  by 
  Stoliczka 
  for 
  some 
  elongated 
  forms 
  of 
  Petricola, 
  which 
  

   burrow 
  in 
  sand 
  or 
  peat, 
  and 
  have 
  generallj^ 
  a 
  full 
  complement 
  of 
  

   teetli, 
  three 
  in 
  the 
  left 
  valve 
  and 
  two 
  in 
  the 
  right. 
  

  

  With 
  regard 
  to 
  Lucinopsis, 
  there 
  is 
  no 
  doubt 
  as 
  to 
  the 
  type, 
  which 
  

   is 
  the 
  Venus 
  undata 
  of 
  Pennant, 
  but 
  there 
  is 
  much 
  difference 
  of 
  

   opinion 
  as 
  to 
  the 
  generic 
  name 
  which 
  this 
  type 
  should 
  connote. 
  The 
  

   facts 
  are 
  as 
  follows. 
  By 
  the 
  earlier 
  conchologists, 
  except 
  Leach, 
  the 
  

   V. 
  undata. 
  Pen., 
  was 
  referred 
  either 
  to 
  Venus 
  or 
  Lucina, 
  and 
  the 
  name 
  

   Lucinopsis 
  was 
  not 
  given 
  to 
  it 
  till 
  1853.^ 
  Long 
  before 
  this, 
  however, 
  

   between 
  the 
  years 
  1816 
  and 
  1818, 
  Dr. 
  W. 
  E. 
  Leach 
  appears 
  to 
  have 
  

   written 
  out 
  a 
  list 
  of 
  British 
  MoUusca, 
  and 
  to 
  have 
  separated 
  some 
  of 
  

  

  ^ 
  Syst. 
  des 
  An. 
  sans 
  Vert., 
  p. 
  121. 
  

  

  * 
  By 
  Forbes 
  & 
  Hanley, 
  British 
  Mollusca, 
  vol. 
  i, 
  p. 
  433. 
  

  

  