﻿Report 
  of 
  the 
  State 
  Geologist. 
  

  

  815 
  

  

  cation 
  in 
  any 
  growth- 
  stage 
  of 
  a 
  deltidium, 
  but 
  the 
  pedicle- 
  

   passage 
  formed 
  by 
  the 
  ultimate 
  union 
  of 
  the 
  valves 
  at 
  

   their 
  cardinal 
  extremities 
  remains 
  uncovered 
  until 
  a 
  comparatively 
  

   late 
  stage. 
  By 
  removing 
  the 
  shell 
  from 
  adult 
  specimens 
  of 
  

  

  Fig. 
  265. 
  

  

  Fig. 
  266. 
  

  

  Fig. 
  267. 
  

  

  Fig. 
  265. 
  Delthyrium 
  of 
  a 
  youig 
  Rhynchonella. 
  

  

  Fig. 
  266. 
  The 
  same, 
  at 
  a 
  later 
  stage, 
  with 
  two 
  triangular 
  deltaria. 
  

  

  Fig. 
  267. 
  The 
  same, 
  at 
  completed 
  growth 
  of 
  the 
  deltaria. 
  

  

  Fig. 
  268 
  Fig. 
  269. 
  

  

  Figs. 
  2c8, 
  269. 
  Dorsal 
  and 
  profile 
  views 
  of 
  Magellania 
  flavescens; 
  showing 
  deltaria 
  and'pedicle. 
  

  

  Fig. 
  270. 
  

  

  Fig. 
  271. 
  

  

  Fig. 
  270. 
  Dorsal 
  view 
  of 
  the 
  umbonal 
  portion 
  of 
  an 
  adult 
  Terebratulina 
  septentrionalis, 
  with 
  

   the 
  shell 
  removed 
  by 
  acid; 
  showing 
  slight 
  secondary 
  extensions 
  of 
  the 
  ventral 
  

   mantle 
  at 
  the 
  base 
  of 
  the 
  pedicle, 
  small 
  deltaria 
  only 
  being 
  formed 
  in 
  this 
  species. 
  

  

  Fig. 
  271. 
  A 
  similar 
  preparation 
  of 
  Magellania 
  flavescens; 
  showing 
  the 
  complete 
  envelopment 
  of 
  

   the 
  base 
  of 
  the 
  pedicle 
  by 
  secondary 
  expansions 
  of 
  the 
  ventral 
  mantle, 
  which 
  have 
  

   formed 
  the 
  deltaria, 
  as 
  shown 
  in 
  fig. 
  268. 
  (Beecher.) 
  

  

  Teeebb 
  itulina 
  and 
  Magellania 
  in 
  which 
  the 
  deltaria 
  have 
  

   become 
  more 
  or 
  less 
  completely 
  developed, 
  it 
  has 
  been 
  found 
  

   that 
  these 
  plates 
  are 
  derived 
  from 
  two 
  secondary 
  expansions 
  of 
  

   the 
  mantle 
  of 
  the 
  pedicle-valve 
  enveloping 
  the 
  base 
  of 
  the 
  pedicle.* 
  

  

  Beecher, 
  loc. 
  cit. 
  

  

  