﻿814 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  corresponding 
  plate 
  has 
  developed 
  on 
  the 
  outer 
  surface 
  of 
  the 
  

   ventral 
  mantle 
  lobe, 
  and 
  between 
  the 
  inner 
  edges 
  of 
  these 
  two 
  

   plates 
  lies 
  the 
  great 
  pedicle 
  which 
  bears 
  on 
  its 
  dorsal 
  side 
  a 
  third 
  

   plate, 
  meeting 
  the 
  dorsal, 
  but 
  widely 
  separated 
  from 
  the 
  

   ventral 
  plate. 
  This 
  third 
  plate 
  is 
  the 
  incipient 
  deltidium. 
  The 
  

   deltidium 
  is, 
  thus, 
  not 
  a 
  secretion 
  from 
  the 
  mantle, 
  but 
  from 
  the 
  

   body 
  of 
  the 
  embryo, 
  and 
  it 
  has 
  been 
  shown 
  tha,t 
  the 
  shell- 
  puncta- 
  

  

  Fig. 
  259. 
  

  

  Fig. 
  261. 
  

  

  Fig. 
  263. 
  

  

  Fig. 
  260. 
  

  

  Fig. 
  262. 
  

  

  Fig. 
  264. 
  

  

  Cisiella 
  Neapolitana. 
  

  

  Fig. 
  259. 
  The 
  complete 
  cephalula 
  stage. 
  

  

  Fig. 
  260. 
  Longitudinal 
  section 
  of 
  same; 
  the 
  shell-secreting 
  surfaces 
  are 
  represented 
  by 
  heavy 
  

   lines. 
  

  

  Fig. 
  261. 
  The 
  larva 
  after 
  inversion 
  of 
  the 
  mantle 
  lobes. 
  

  

  Fig. 
  262. 
  Longitudinal 
  section 
  based 
  on 
  the 
  preceding. 
  The 
  shell 
  bearing 
  surfaces 
  arenow 
  on 
  

   the 
  outside 
  of 
  the 
  animal, 
  the 
  large 
  pedicle 
  extending 
  upward. 
  

  

  Figs. 
  263, 
  264. 
  Dorsal 
  and 
  profile 
  views 
  of 
  a 
  very 
  young 
  shell 
  ; 
  showing 
  the 
  large 
  poste 
  rior 
  open- 
  

   ing 
  between 
  the 
  valves 
  and 
  the 
  thick 
  pedicle. 
  

  

  (Beecher; 
  adapted 
  from 
  Kowalevski 
  and 
  Shipley.) 
  

  

  tions, 
  which 
  are 
  usually 
  present 
  in 
  the 
  valves 
  of 
  the 
  deltidium- 
  

   bearing 
  species, 
  such 
  as 
  Leptcena 
  rhomboidalis, 
  Chonetes 
  scitula 
  y 
  

   etc., 
  do 
  not 
  exist 
  in 
  the 
  deltidium.* 
  

  

  In 
  the 
  corresponding 
  stages 
  of 
  growth 
  in 
  Cistella 
  and 
  

   Terebra.tulina, 
  'there 
  is 
  no 
  evidence 
  of 
  this 
  body- 
  plate, 
  no 
  indi- 
  

  

  * 
  In 
  Aulosteges 
  the 
  surface 
  of 
  the 
  de'tidium 
  is 
  covered 
  with 
  short 
  spinules 
  or 
  tubercles. 
  

   Such 
  spinules 
  in 
  the 
  productoids 
  imply 
  a 
  punctation 
  of 
  the 
  shell, 
  wherever 
  occurring 
  on 
  the 
  

   valves, 
  but 
  an 
  examination 
  of 
  the 
  deltidium 
  in 
  this 
  genus 
  indicates 
  that 
  the 
  secondary 
  modifi- 
  

   cation 
  of 
  the 
  surface 
  of 
  the 
  deltidium 
  is 
  not 
  accompanied 
  with 
  a 
  punctate 
  structure. 
  

  

  