﻿1038 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  vertical 
  septa, 
  and 
  extend 
  for 
  some 
  distance 
  in 
  front 
  of 
  them. 
  

   They 
  are 
  divided 
  by 
  a 
  low 
  axial 
  ridge. 
  

  

  Shell-substance 
  fibrous, 
  impunctate. 
  

  

  Type, 
  Conchidium 
  biloculare, 
  Linne 
  (=Gypidia 
  or 
  Pentamerus 
  

   conchidium, 
  Dalman 
  et 
  al. 
  Upper 
  Silurian 
  limestone, 
  Gotland.) 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Devonian. 
  

  

  Pentamerus, 
  Sowerby. 
  1813. 
  

   (Plate 
  47, 
  figs. 
  1-9.) 
  

   Smooth 
  shells, 
  of 
  variable 
  contour, 
  sometimes 
  bearing 
  a 
  few 
  

   broad 
  and 
  obscure 
  radiating 
  undulations. 
  There 
  is 
  no 
  median 
  

   fold 
  and 
  sinus, 
  though 
  a 
  median 
  prolongation 
  of 
  the 
  valves, 
  

   defined 
  by 
  two 
  divergent 
  lateral 
  furrows, 
  is 
  a 
  normal 
  character. 
  

   A 
  concave 
  deltidium 
  is 
  sometimes 
  retained, 
  and 
  a 
  faint 
  lobation 
  

  

  Fig. 
  453. 
  Fig. 
  454. 
  Fig. 
  455. 
  Fig. 
  456. 
  

  

  Fig. 
  453. 
  Pentamerus 
  oblongus, 
  Sowerby. 
  A 
  transverse 
  section, 
  showing 
  the 
  septa. 
  

  

  Figs. 
  454, 
  455. 
  Transverse 
  sections 
  of 
  the 
  septa 
  of 
  Pentamerus 
  oblongus. 
  Fig. 
  454 
  shows 
  the 
  

   septum 
  of 
  the 
  pedicle- 
  valve 
  and 
  the 
  inclosure 
  of 
  its 
  base 
  by 
  the 
  shell-substance 
  

   of 
  The 
  valve. 
  Fig. 
  455 
  is 
  an 
  enlargement 
  of 
  the 
  septa 
  of 
  the 
  brachial 
  valve, 
  and 
  

   shows 
  a 
  thin 
  coating 
  of 
  testaceous 
  matter 
  upon 
  tha 
  inner 
  faces 
  of 
  the 
  prismatic 
  

   walls. 
  

  

  Fig. 
  456. 
  Pentamerus 
  cylindricus, 
  Hall. 
  A 
  transverse 
  section, 
  showing 
  the 
  septa. 
  

  

  of 
  the 
  apical 
  end 
  of 
  the 
  spondylium 
  is 
  the 
  sole 
  evidence 
  of 
  a 
  car- 
  

   dinal 
  process. 
  The 
  depth 
  of 
  the 
  spondylium 
  and 
  septal 
  cavity 
  

   varies 
  with 
  the 
  convexity 
  of 
  the 
  valves. 
  Sometimes 
  the 
  septa 
  

   unite 
  before 
  reaching 
  the 
  inner 
  surface 
  of 
  the 
  brachial 
  valve 
  and 
  

   the 
  spondylium 
  thus 
  formed 
  is 
  supported 
  by 
  a 
  low 
  axial 
  septum. 
  

  

  Type, 
  Pentamerus 
  oblongus, 
  Sowerby. 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Lower 
  Devonian. 
  

  

  Barrandella, 
  Hall. 
  1893. 
  

   Synonym; 
  Olorinda, 
  Barrande, 
  1879. 
  

   (Plate 
  48, 
  figs. 
  1-5.) 
  

   Galeatiform 
  pentameroicls 
  with 
  median 
  fold 
  on 
  the 
  brachial 
  

   valve 
  and 
  median 
  sinus 
  on 
  the 
  pedicle- 
  valve. 
  Shells 
  small, 
  sur- 
  

   face 
  smooth 
  or 
  rarely 
  plicate. 
  

  

  96 
  

  

  