﻿EXPLANATION 
  OF 
  PLATE 
  IV. 
  

  

  Plum 
  a 
  lin 
  a 
  plumaria 
  Hall. 
  

   Page 
  255. 
  

  

  Fig. 
  1. 
  A 
  branching 
  frond, 
  which 
  apparently 
  has 
  been 
  imbedded 
  while 
  in 
  a 
  grow- 
  

   ing 
  and 
  vigorous 
  condition 
  ; 
  all 
  the 
  pinnuhe 
  holdiug 
  their 
  position 
  and 
  

   attachment. 
  

  

  Fig. 
  2. 
  Enlargement 
  of 
  a 
  specimen 
  showing 
  a 
  portion 
  of 
  the 
  rachis 
  denuded 
  of 
  its 
  

   pinnulaa, 
  except 
  two 
  at 
  the 
  upper 
  extremity. 
  

  

  The 
  apparent 
  annulation 
  is 
  an 
  exaggeration 
  of 
  the 
  characters 
  of 
  the 
  

   rachis 
  and 
  incorrectly 
  represents 
  the 
  fossil. 
  

  

  Fig. 
  3. 
  A 
  frond 
  which 
  is 
  somewhat 
  dilapidated, 
  apparently 
  from 
  maceration 
  and 
  

   decay, 
  while 
  lying 
  upon 
  the 
  sea 
  bottom. 
  The 
  midrib 
  and 
  pinnulse 
  show 
  

   the 
  attachment 
  of 
  numerous 
  germs 
  and 
  young 
  (some 
  of 
  them 
  perhaps 
  

   still 
  in 
  the 
  form 
  of 
  eggs) 
  of 
  a 
  Brachiopod 
  of 
  the 
  genus 
  Rhynchonella 
  

   or 
  Stenocisma. 
  The 
  smaller 
  forms 
  present 
  merely 
  flattened 
  spheroidal 
  

   or 
  ovate 
  bodies, 
  which 
  in 
  farther 
  development 
  sbow 
  slight 
  evidence 
  of 
  

   inequalities 
  of 
  the 
  surface, 
  which 
  in 
  a 
  later 
  stage 
  become 
  obscure 
  plica- 
  

   tions. 
  The 
  pinnulae, 
  from 
  maceration, 
  gradually 
  fall 
  off, 
  leaving 
  the 
  

   rachis 
  free, 
  when 
  these 
  germs 
  acquire 
  a 
  farther 
  development, 
  as 
  shown 
  

   in 
  figures 
  4 
  and 
  5. 
  

  

  Fig. 
  4. 
  A 
  part 
  of 
  the 
  rachis 
  of 
  a 
  specimen 
  denuded 
  of 
  its 
  pinnulss, 
  and 
  preserving 
  

   the 
  young 
  brachiopod 
  still 
  attached. 
  Natural 
  size. 
  

  

  Fig. 
  5. 
  A 
  similar 
  specimen 
  where 
  the 
  rachis, 
  has 
  been 
  bent 
  and 
  recurved 
  upon 
  

   itself, 
  preserving 
  the 
  brachiopods 
  still 
  attached. 
  

  

  These 
  specimens 
  are 
  from 
  the 
  shales 
  of 
  the 
  Portage 
  group. 
  

  

  Plumaltna 
  dens 
  a 
  n. 
  sp. 
  

  

  Fig. 
  6. 
  A 
  fragment 
  of 
  a 
  frond, 
  natural 
  size, 
  in 
  which 
  the 
  rachis 
  is 
  less 
  rigid 
  and 
  

   distinct, 
  the 
  pinnules 
  narrower, 
  proportional 
  ry 
  longer, 
  and 
  more 
  crowded 
  

   than 
  in 
  the 
  preceding 
  form. 
  

   From 
  the 
  shales 
  of 
  the 
  Hamilton 
  group. 
  

  

  