﻿JUKES-BROWNE 
  : 
  ON 
  THE 
  FAMILY 
  PETEICOLIDiE. 
  219 
  

  

  equally 
  inflated 
  at 
  each 
  end 
  ; 
  in 
  fact, 
  it 
  differs 
  in 
  shape 
  from 
  any 
  

   other 
  species 
  either 
  of 
  Petricolaria 
  or 
  Rupellaria, 
  and 
  its 
  hinge 
  is 
  more 
  

   regular 
  with 
  the 
  teeth 
  more 
  divergent. 
  

  

  Lajonkairea. 
  — 
  The 
  shells 
  of 
  L. 
  Lajojilcairea 
  and 
  L. 
  substriata 
  also 
  

   differ 
  in 
  shape 
  from 
  any 
  of 
  the 
  Petricola 
  and 
  Rupellaria 
  group, 
  being 
  

   short 
  and 
  subquadrate, 
  the 
  posterior 
  portion 
  being 
  higher 
  than 
  the 
  

   anterior, 
  while 
  the 
  reverse 
  is 
  the 
  case 
  in 
  Petricola. 
  The 
  hinge, 
  

   however, 
  is 
  of 
  similar 
  construction, 
  having 
  three 
  teeth 
  in 
  the 
  left 
  

   valve, 
  the 
  median 
  being 
  widely 
  bifid, 
  and 
  only 
  two 
  in 
  the 
  right 
  valve 
  ; 
  

   but 
  the 
  teeth 
  are 
  more 
  widely 
  divergent 
  than 
  in 
  Petricola. 
  The 
  

   ligament 
  is 
  well 
  developed, 
  but 
  is 
  sunk 
  between 
  the 
  valves 
  so 
  as 
  to 
  be 
  

   hardly 
  visible 
  from 
  outside. 
  The 
  pallial 
  sinus 
  is 
  large, 
  broad, 
  and 
  

   ascending. 
  The 
  margins 
  of 
  the 
  valves 
  are 
  smooth 
  in 
  spite 
  of 
  the 
  

   strong 
  external 
  radial 
  riblets. 
  

  

  Thus 
  there 
  is 
  no 
  doubt 
  that, 
  judging 
  from 
  the 
  shell 
  alone. 
  Gray 
  was 
  

   right 
  in 
  placing 
  Lajonlcairea 
  in 
  the 
  Petricolidse. 
  At 
  the 
  same 
  time 
  

   Wood 
  & 
  Fischer 
  were 
  equally 
  justified 
  in 
  considering 
  it 
  as 
  closely 
  

   allied 
  to 
  Lucinopsis, 
  and 
  therefore 
  I 
  cannot 
  agree 
  with 
  Dr. 
  Dall 
  in 
  

   regarding 
  it 
  merely 
  as 
  a 
  Rupellaria, 
  and 
  not 
  worthy 
  of 
  separation 
  

   from 
  Petricola. 
  

  

  Moreover, 
  Mons. 
  A. 
  Dollfus 
  assures 
  me 
  that 
  Lajonkairea 
  is 
  not 
  

   a 
  boring 
  mollusc. 
  It 
  generally 
  lives 
  in 
  sand 
  or 
  other 
  soft 
  material, 
  

   and 
  its 
  shell 
  is 
  then 
  quite 
  regular, 
  but 
  sometimes 
  it 
  harbours 
  in 
  the 
  

   borings 
  of 
  other 
  molluscs, 
  and 
  then 
  its 
  shell 
  becomes 
  more 
  or 
  less 
  

   irregular 
  and 
  deformed. 
  

  

  Lucinopsis. 
  — 
  The 
  type 
  of 
  this 
  genus 
  has 
  a 
  thin 
  suborbicular 
  shell, 
  

   nearly 
  smooth, 
  and 
  only 
  marked 
  by 
  concentric 
  lines 
  of 
  growth. 
  The 
  

   posterior 
  part 
  is 
  higher 
  and 
  larger 
  than 
  the 
  anterior 
  part. 
  The 
  

   ligament 
  is 
  externally 
  very 
  long 
  and 
  clearly 
  visible 
  from 
  the 
  outside, 
  

   being 
  only 
  slightly 
  sunk 
  between 
  the 
  valves. 
  There 
  is 
  no 
  lunule 
  nor 
  

   escutcheon. 
  

  

  Inside 
  there 
  is 
  a 
  fairly 
  broad 
  hinge-plate 
  bearing 
  in 
  the 
  left 
  valve 
  

   three 
  close-set 
  but 
  divergent 
  teeth, 
  the 
  central 
  one 
  of 
  which 
  is 
  deeply 
  

   and 
  broadly 
  bifid 
  ; 
  in 
  the 
  right 
  valve 
  there 
  are 
  two 
  divergent 
  teeth 
  

   which 
  are 
  respectively 
  posterior 
  and 
  central, 
  and 
  sometimes 
  the 
  

   rudiment 
  of 
  an 
  anterior 
  cardinal 
  can 
  be 
  seen 
  in 
  front 
  of 
  the 
  latter. 
  

   The 
  pallial 
  sinus 
  is 
  large, 
  deep, 
  and 
  ascending, 
  but 
  rounded 
  at 
  the 
  end. 
  

  

  Prom 
  the 
  above 
  description 
  it 
  will 
  be 
  seen 
  that 
  the 
  internal 
  

   characters 
  of 
  Lucinopsis 
  are 
  substantially 
  those 
  of 
  Petricola 
  and 
  

   Lajonlcairea 
  ; 
  but 
  the 
  great 
  difference 
  in 
  the 
  shape 
  and 
  texture 
  of 
  the 
  

   shell 
  seems 
  hitherto 
  to 
  have 
  prevented 
  conchologists 
  from 
  perceiving 
  

   its 
  real 
  affinities. 
  It 
  is 
  surprising 
  that 
  Fischer, 
  having 
  gone 
  so 
  far 
  as 
  

   to 
  group 
  Lajonkairea 
  as 
  a 
  sub-genus 
  of 
  Lucinopsis, 
  did 
  not 
  realize 
  that 
  

   both 
  of 
  them 
  were 
  more 
  akin 
  to 
  Petricola 
  than 
  to 
  Venerupis 
  or 
  

   dementia. 
  

  

  Veneritapes. 
  — 
  It 
  has 
  recently 
  come 
  to 
  my 
  knowledge 
  that 
  the 
  little 
  

   Eocene 
  shell, 
  described 
  by 
  M. 
  Cossmann 
  in 
  1886 
  ^ 
  as 
  the 
  type 
  of 
  a 
  new 
  

   genus 
  under 
  the 
  name 
  of 
  Veneritapes, 
  is 
  closely 
  allied 
  to 
  Lucinopsis. 
  

  

  1 
  Ann. 
  Soc. 
  Hoy. 
  Make, 
  lielge, 
  vol. 
  xxi, 
  p. 
  104. 
  

  

  