﻿JTJKES-BROWNE 
  : 
  ON 
  THE 
  FAMILY 
  PETRICOLID^. 
  217 
  

  

  by 
  Billborg 
  for 
  an 
  insect, 
  so 
  that 
  the 
  well-known 
  name 
  Diplodonta 
  can 
  

   be 
  retained 
  for 
  Tellina 
  roUmdata 
  and 
  its 
  allies. 
  

  

  With 
  regard 
  to 
  Claudico7icha, 
  the 
  only 
  species 
  actually 
  mentioned 
  

   by 
  Fischer 
  in 
  his 
  Manuel 
  is 
  Venerupis 
  mo7isirosa 
  (Chem.), 
  which 
  

   consequently 
  must 
  be 
  taken 
  as 
  the 
  type. 
  1 
  shall 
  also 
  have 
  occasion 
  to 
  

   discuss 
  the 
  Veneritapes 
  of 
  Cossmann, 
  founded 
  in 
  1886 
  on 
  the 
  Vemcs 
  

   Bervillei 
  of 
  Deshayes. 
  

  

  Coo'perella 
  is 
  auotlier 
  shell 
  which 
  may 
  have 
  to 
  be 
  included 
  in 
  the 
  

   Petficolidse, 
  and 
  the 
  type 
  of 
  this 
  is 
  C. 
  diapliana, 
  Carp. 
  According 
  to 
  

   Dr. 
  Dall,' 
  who 
  has 
  examined 
  the 
  types, 
  Carpenter 
  - 
  originally 
  described 
  

   two 
  varieties 
  of 
  the 
  same 
  species 
  as 
  distinct 
  sections 
  or 
  sub-genera, 
  

   calling 
  one 
  v^dalia 
  and 
  the 
  other 
  Cooperella, 
  and 
  regai'ding 
  the 
  former 
  

   as 
  the 
  generic 
  type 
  ; 
  but 
  as 
  the 
  name 
  ^dalia 
  is 
  preoccupied, 
  that 
  of 
  

   Cooperella 
  must 
  stand 
  for 
  the 
  genus. 
  The 
  supposed 
  differences 
  consist 
  

   only 
  in 
  the 
  degree 
  to 
  which 
  the 
  resilium 
  is 
  sunk, 
  and 
  in 
  the 
  bifidity 
  

   of 
  the 
  teeth, 
  the 
  extent 
  of 
  which 
  varies 
  in 
  different 
  individuals. 
  

  

  At 
  present 
  only 
  one 
  species 
  of 
  Cooperella 
  is 
  known, 
  and 
  that 
  is 
  

   a 
  common 
  shell 
  on 
  the 
  Californian 
  coast, 
  but 
  Dr. 
  Dall 
  has 
  described 
  a 
  

   species 
  from 
  the 
  Miocene 
  of 
  Virginia, 
  so 
  that 
  formerly 
  it 
  inhabited 
  the 
  

   Atlantic 
  Ocean 
  as 
  well 
  as 
  the 
  Pacific. 
  

  

  2. 
  Description 
  of 
  Shells. 
  

  

  Petricola 
  and 
  Rupellaria. 
  — 
  A 
  general 
  description 
  applicable 
  to 
  both 
  

   of 
  these 
  may 
  be 
  given, 
  because 
  both 
  are 
  boring 
  molluscs 
  and 
  clearly 
  

   belong 
  to 
  the 
  same 
  genus. 
  

  

  In 
  consequence 
  of 
  the 
  boring 
  habit 
  the 
  external 
  shape 
  and 
  sculpture 
  

   of 
  the 
  shell 
  varies 
  much 
  in 
  different 
  species 
  ; 
  but 
  excluding 
  Petricolaria, 
  

   they 
  are 
  either 
  oval 
  or 
  pyriform 
  ; 
  there 
  is 
  no 
  lunule 
  nor 
  escutcheon 
  ; 
  

   the 
  ligament 
  is 
  external 
  but 
  generally 
  sunk 
  between 
  the 
  hinge-plates. 
  

   The 
  internal 
  characters 
  are 
  more 
  definite, 
  though 
  from 
  the 
  descriptions 
  

   given 
  by 
  different 
  authors 
  it 
  might 
  be 
  thought 
  that 
  they 
  were 
  not. 
  

   Thus 
  Gray 
  could 
  find 
  only 
  two 
  teeth 
  in 
  each 
  valve 
  ; 
  Woodward 
  

   says 
  "hinge 
  with 
  three 
  teeth 
  in 
  each 
  valve", 
  a 
  statement 
  which 
  is 
  

   difficult 
  to 
  explain 
  ; 
  the 
  Messrs. 
  Adams 
  follow 
  Gray 
  in 
  making 
  two 
  

   teeth 
  in 
  each 
  valve, 
  " 
  one 
  of 
  which 
  is 
  often 
  obsolete," 
  and 
  Fischer 
  

   describes 
  the 
  hinge 
  as 
  " 
  carrying 
  two 
  divergent 
  cardinal 
  teeth 
  in 
  each 
  

   valve, 
  the 
  posterior 
  right 
  and 
  the 
  anterior 
  left 
  being 
  bifid", 
  but 
  he 
  

   adds 
  " 
  sometimes 
  a 
  rudiment 
  of 
  a 
  third 
  tooth 
  ". 
  

  

  The 
  real 
  fact 
  is 
  that 
  the 
  normal 
  number 
  of 
  teeth 
  is 
  three 
  in 
  the 
  left 
  

   valve 
  and 
  two 
  in 
  the 
  right, 
  and 
  Dr. 
  Dall 
  has 
  rightly 
  recognized 
  this 
  as 
  

   the 
  true 
  dentition 
  of 
  the 
  genus. 
  ^ 
  There 
  is 
  a 
  tendency 
  for 
  the 
  teeth 
  

   to 
  become 
  irregular 
  and 
  obsolete, 
  as 
  is 
  so 
  often 
  the 
  case 
  in 
  boring 
  

   Mollusca, 
  so 
  that 
  the 
  number 
  varies 
  in 
  different 
  individuals 
  and 
  in 
  

   different 
  species. 
  In 
  such 
  circumstances 
  young 
  shells 
  should 
  be 
  

   examined, 
  and 
  the 
  species 
  which 
  exhibit 
  the 
  larger 
  number 
  and 
  

   most 
  regular 
  arrangement 
  of 
  teeth 
  should 
  be 
  regarded 
  as 
  representing 
  

   the 
  normal 
  dentition. 
  

  

  ' 
  Trans. 
  Wagner 
  Free 
  Inst. 
  Sc, 
  vol. 
  iii, 
  pt. 
  v, 
  p. 
  1062, 
  1900. 
  

  

  2 
  Rep. 
  Brit. 
  Assoc, 
  for 
  1863, 
  pp. 
  611, 
  639. 
  

  

  •' 
  Trans. 
  Wagner 
  Free 
  Inst. 
  Sc, 
  vol. 
  iii, 
  pt. 
  v, 
  p. 
  1056, 
  1900. 
  

  

  