﻿1110 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  they 
  may 
  all 
  be 
  safely 
  included 
  under 
  the 
  old 
  family 
  designation 
  

   introduced 
  by 
  Kutorga 
  in 
  1848, 
  Siphonotretidm. 
  

  

  Crania 
  and 
  its 
  allies 
  (Craniella, 
  Psettdoorania, 
  Pholtdops) 
  

   constitute 
  a 
  group 
  in 
  which, 
  thus 
  far, 
  there 
  is 
  no 
  satisfactory 
  evi- 
  

   dence 
  of 
  the 
  existence 
  of 
  the 
  pedicle, 
  and 
  we 
  are 
  left 
  to 
  the 
  assump- 
  

   tion 
  that 
  this 
  organ 
  became 
  atrophied 
  at 
  a 
  very 
  early 
  growth-stage. 
  

   The 
  study 
  of 
  recent 
  Crania 
  s 
  has 
  not 
  yet 
  determined 
  this 
  point, 
  but 
  

   will 
  probably 
  ultimately 
  accomplish 
  this 
  end. 
  At 
  whatever 
  stage 
  

   of 
  growth 
  the 
  pedicle 
  was 
  lost, 
  we 
  may 
  infer 
  that 
  its 
  disappear- 
  

   ance 
  was 
  directly 
  followed^ 
  in 
  Crania, 
  and 
  generally 
  in 
  Cra- 
  

   niblla, 
  by 
  a 
  solid 
  fixation 
  of 
  the 
  animal 
  by 
  the 
  substance 
  of 
  one 
  

   of 
  the 
  valves. 
  In 
  Pholidops 
  there 
  was 
  no 
  such 
  cementation, 
  but 
  

   at 
  a 
  correspondingly 
  early 
  stage 
  the 
  shell 
  became 
  wholly 
  inde- 
  

   pendent. 
  All 
  these 
  shells 
  with 
  central 
  or 
  subcentral 
  beaks 
  have 
  

   an 
  external 
  resemblance 
  to 
  Orbiculoidea 
  ; 
  the 
  formation 
  of 
  the 
  

   secondary 
  growth 
  of 
  the 
  valves 
  behind 
  the 
  apices 
  or 
  position 
  of 
  

   the 
  protoconch, 
  is 
  a 
  further 
  substantial 
  agreement 
  with 
  the 
  Dia- 
  

   caulia 
  as 
  contrasted 
  with 
  the 
  abbreviated 
  posterior 
  peripheral 
  

   shell-growth 
  in 
  the 
  Mesocatjlia 
  (Lingula, 
  Oboltjs). 
  It 
  is 
  never- 
  

   theless 
  to 
  be 
  observed 
  that 
  no 
  trace 
  is 
  found 
  on 
  mature 
  or 
  imma- 
  

   ture 
  shells, 
  of 
  a 
  former 
  pedicle-slit, 
  incision 
  or 
  perforation, 
  and 
  it 
  

   would 
  be 
  difficult 
  to 
  comprehend 
  in 
  what 
  manner 
  such 
  an 
  essen- 
  

   tial 
  modification 
  of 
  the 
  shell 
  could 
  be 
  wholly 
  concealed 
  by 
  later 
  

   growth.* 
  Were 
  the 
  pedicle 
  marginal 
  in 
  primitive 
  growth-stages, 
  

   and 
  subsequently 
  atrophied, 
  the 
  obliteration 
  of 
  the 
  marginal 
  

   opening 
  by 
  later 
  resorption 
  and 
  growth 
  would 
  be 
  a 
  readily 
  intel- 
  

   ligible 
  process. 
  There 
  is, 
  hence, 
  in 
  this 
  default 
  of 
  evidence, 
  a 
  

   good 
  reason 
  to 
  doubt 
  the 
  close 
  affinities 
  of 
  Crania 
  and 
  Pholidops 
  

   to 
  the 
  Diacaulia. 
  Present 
  knowledge 
  would 
  seem 
  to 
  indicate 
  

   that 
  they 
  were 
  primarily 
  of 
  the 
  type 
  of 
  the 
  Mesocatjlia, 
  and 
  that 
  

   their 
  resemblance 
  to 
  the 
  Diacaulia 
  is 
  wholly 
  of 
  secondary 
  

   growth.f 
  Waagen's 
  term 
  for 
  this 
  group 
  Gasteropegmata 
  (or 
  

   Craniacea), 
  may 
  therefore 
  prove 
  to 
  be 
  equivalent 
  to 
  each 
  of 
  

   these 
  other 
  two 
  divisions. 
  

  

  * 
  Quite 
  early 
  conditions 
  of 
  Crania 
  siluriana 
  and 
  Craniella 
  Hamiltonice, 
  from 
  1.5 
  to 
  .5 
  mm. 
  

   in 
  diameter, 
  are 
  fully 
  cemented. 
  Examples 
  of 
  Pholidops 
  Hamiltonice, 
  not 
  above 
  .5 
  mm. 
  in 
  

   diameter, 
  give 
  no 
  indication 
  of 
  a 
  pedicle-passage 
  or 
  surface 
  characters 
  not 
  present 
  in 
  the 
  adult. 
  

  

  t 
  Some 
  species 
  of 
  Pholidops 
  (P. 
  arenaria, 
  P. 
  linguloides) 
  have 
  a 
  terminal 
  submarginal 
  

   apex; 
  and 
  their 
  resemblance 
  exteriorly 
  to 
  the 
  oboloids 
  is 
  very 
  striking. 
  This 
  is, 
  however, 
  no 
  

   more 
  than 
  a 
  resemblance, 
  as 
  they 
  show, 
  on 
  the 
  under 
  side, 
  the 
  same 
  mode 
  of 
  peripheral 
  

   growth 
  beneath 
  the 
  beak 
  as 
  the 
  other 
  forms 
  of 
  the 
  genus 
  in 
  which 
  the 
  umbones 
  are 
  more 
  

   nearly 
  central. 
  

  

  168 
  

  

  