﻿Report 
  of 
  the 
  State 
  Geologist. 
  947 
  

  

  The 
  cardinal 
  ^process 
  is 
  a 
  low, 
  transverse, 
  sessile 
  apophysis, 
  

   having 
  its 
  surface 
  vertically 
  striated 
  ; 
  occasionally 
  it 
  is 
  bipartite 
  

   or 
  it 
  may 
  be 
  wholly 
  resorbed. 
  

  

  The 
  crura 
  are 
  long, 
  straight 
  and 
  slightly 
  divergent; 
  their 
  

   union 
  with 
  the 
  primary 
  lamellae 
  of 
  the 
  spiral 
  ribbon 
  is 
  at 
  

   a 
  broadly 
  obtuse 
  angle. 
  The 
  brachial 
  coils 
  are 
  directed 
  

   outward 
  and 
  upward 
  toward 
  the 
  cardinal 
  angles 
  of 
  the 
  valves, 
  

   and 
  their 
  variation 
  in 
  size 
  and 
  direction 
  is 
  in 
  keeping 
  with 
  the 
  

   differences 
  in 
  the 
  marginal 
  outline 
  of 
  the 
  shell. 
  The 
  number 
  

   of 
  volutions 
  of 
  the 
  ribbon 
  exceeds 
  that 
  in 
  any 
  other 
  genus 
  of 
  

   brachiopods. 
  There 
  is 
  no 
  jugum 
  ; 
  its 
  position, 
  however, 
  is 
  indi- 
  

   cated 
  by 
  a 
  pair 
  of 
  short 
  spinous 
  processes 
  originating 
  on 
  the 
  

   primary 
  lamellae 
  soon 
  after 
  their 
  junction 
  with 
  the 
  crura, 
  and 
  

   which 
  are 
  directed 
  inward 
  with 
  a 
  slight 
  convergence. 
  

  

  The 
  muscular 
  area 
  has 
  about 
  the 
  same 
  extent 
  as 
  that 
  of 
  the 
  

   pedicle-valve, 
  though 
  less 
  distinctly 
  impressed 
  and 
  generally 
  more 
  

   elongated. 
  It 
  is 
  constituted 
  of 
  two 
  pairs 
  of 
  adductor 
  impressions 
  

   with 
  their 
  surfaces 
  radiately 
  or 
  palmately 
  striated. 
  The 
  anterior 
  

   pair 
  are 
  central, 
  narrow 
  at 
  their 
  posterior 
  extremities 
  which 
  are 
  

   embraced 
  by 
  the 
  broader 
  posterior 
  scars. 
  

  

  A 
  faint 
  median 
  septum 
  is 
  sometimes 
  present. 
  In 
  some 
  

   instances 
  of 
  importance 
  the 
  socket 
  walls 
  are 
  supported 
  by 
  septa 
  

   which 
  may 
  be 
  considerably 
  produced 
  over 
  the 
  bottom 
  of 
  the 
  

   valve. 
  

  

  In 
  both 
  valves 
  the 
  genital 
  region 
  is 
  distinctly 
  punctated, 
  but 
  

   vascular 
  markings 
  are 
  rarely 
  observed. 
  

  

  Type, 
  A?,omites 
  striatus, 
  Martin 
  (1809). 
  Carboniferous 
  lime- 
  

   stone. 
  

  

  This 
  comprehensive 
  genus 
  has 
  been 
  divided 
  into 
  the 
  following 
  

   sections, 
  based 
  largely 
  upon 
  American 
  species, 
  though 
  it 
  is 
  

   believed 
  that 
  with 
  the 
  addition 
  of 
  some 
  equivalent 
  division 
  

   the 
  grouping 
  will 
  be 
  found 
  generally 
  applicable 
  to 
  all 
  Spirifers. 
  

  

  Section 
  I. 
  Eadiati. 
  (Plate 
  23, 
  figs. 
  1-15.) 
  Typical 
  example, 
  

   Spirifer 
  radiatus, 
  Sowerby 
  (including 
  S. 
  plicatellus, 
  Sowerby). 
  

  

  Smooth, 
  radially 
  undulated 
  or 
  plicated 
  ; 
  fold 
  and 
  sinus 
  smooth; 
  

   entire 
  surface 
  covered 
  with 
  fine, 
  filiform, 
  radiating 
  striae, 
  which 
  

   may 
  be 
  minutely 
  crenulated 
  or 
  granulose. 
  

  

  5 
  

  

  