﻿Report 
  of 
  tee 
  State 
  Geologist. 
  1039 
  

  

  The 
  pedicle-valve 
  bears 
  a 
  short 
  spondylium 
  supported 
  only 
  at 
  

   its 
  posterior 
  surface, 
  the 
  free 
  extension 
  being 
  produced 
  forward 
  

   and 
  upward 
  into 
  the 
  cavity 
  of 
  the 
  opposite 
  valve 
  ; 
  the 
  crural 
  

   plates 
  of 
  the 
  brachial 
  valve 
  are 
  concave 
  on 
  their 
  outer 
  surfaces 
  

   and 
  supported 
  by 
  convergent 
  septa 
  uniting 
  as 
  they 
  reach 
  the 
  

   valve 
  and 
  leaving 
  but 
  a 
  single 
  median 
  line 
  of 
  union 
  on 
  its 
  surface. 
  

  

  Fig. 
  457. 
  Fig. 
  458. 
  

  

  Fig. 
  457. 
  Barrandella 
  linguifera, 
  Sower 
  by. 
  Transverse 
  section 
  near 
  the 
  anterior 
  "extremity 
  

   of 
  the 
  median 
  septum 
  in 
  the 
  pedicle- 
  valve; 
  showing 
  the 
  form 
  of 
  the 
  spondylia. 
  

  

  Fig. 
  458. 
  Barrandella 
  Barrandii, 
  Billings. 
  A 
  transverse 
  section 
  in 
  front 
  of 
  the 
  termination 
  of 
  

   the 
  median 
  septum 
  of 
  the 
  pedicle-valve; 
  showing 
  the 
  form 
  of 
  the 
  spondylium 
  in 
  

   both 
  valves, 
  and 
  the 
  coalescence 
  of 
  the 
  septa 
  in 
  the 
  (lower) 
  brachial 
  valve. 
  

  

  Strong 
  vascular, 
  or 
  ovarian 
  sinuses 
  radiate 
  from 
  the 
  umbonal 
  

   region 
  of 
  the 
  pedicle-valve. 
  These 
  are 
  complicated 
  with 
  the 
  

   undefined 
  diductor 
  scars 
  and 
  are, 
  therefore, 
  to 
  a 
  certain 
  extent, 
  of 
  

   muscular 
  origin. 
  

  

  Type, 
  Barrandella 
  linguifera, 
  Sowerby 
  (sp.). 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Devonian 
  (?). 
  

  

  Pentamerella, 
  Hall. 
  1867. 
  

   (Plate 
  48, 
  figs. 
  6-15.) 
  

  

  Shells 
  with 
  median 
  fold 
  and 
  sinus 
  as 
  in 
  Barrandella, 
  usually 
  

   larger 
  and 
  strongly 
  plicate, 
  possessing 
  a 
  very 
  narrow 
  cardinal 
  

   area, 
  an 
  elongate 
  pseudo-area, 
  and 
  incipient 
  deltidial 
  plates. 
  

   The 
  median 
  septum 
  on 
  the 
  interior 
  of 
  the 
  pedicle-valve 
  is 
  very 
  

   short, 
  and 
  at 
  times 
  is 
  altogether 
  absent. 
  In 
  the 
  brachial 
  valve 
  

   the 
  crural 
  plates 
  and 
  supporting 
  septa 
  form 
  a 
  distinct 
  spondylium 
  

   which 
  is 
  broadly 
  sessile 
  on 
  the 
  surface 
  of 
  the 
  valve. 
  

  

  Type, 
  Pentamerella 
  arata, 
  Conrad 
  (sp.). 
  

  

  Distribution. 
  Devonian. 
  

  

  Sieberella, 
  (Ehlert. 
  1887. 
  

   (Plate 
  48, 
  figs. 
  16-21.) 
  

  

  Galeatiform 
  pentameroids 
  having 
  the 
  median 
  fold 
  on 
  the 
  

   pedicle- 
  valve 
  and 
  the 
  median 
  sinus 
  on 
  the 
  brachial 
  valve. 
  Surface 
  

   plicate 
  without 
  evidence 
  of 
  cardinal 
  area 
  or 
  deltidial 
  plates. 
  

  

  97 
  

  

  