﻿1040 
  Forty- 
  seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  Pedicle- 
  valve 
  with 
  well- 
  developed 
  median 
  sept 
  am, 
  and 
  moderately 
  

   long 
  spondylium 
  which 
  is 
  free 
  for 
  fully 
  two-thirds 
  its 
  length. 
  

   In 
  the 
  brachial 
  valve 
  of 
  typical 
  examples 
  from 
  the 
  Gotland 
  and 
  

   Wenlock 
  limestones 
  no 
  spondylium 
  informed 
  ; 
  the 
  septa 
  support- 
  

   ing 
  the 
  crural 
  plates 
  resting 
  directly 
  on 
  the 
  surface 
  of 
  the 
  valves. 
  

  

  Fig. 
  459". 
  Fig. 
  460. 
  

  

  Fig. 
  461.— 
  Transverse 
  section 
  of 
  Sieberella 
  galeata, 
  near 
  the 
  beaks, 
  the 
  pedicle- 
  valve 
  being 
  

   uppermost; 
  showing 
  the 
  discrete 
  septa 
  of 
  the 
  brachial 
  valve. 
  

  

  Fig. 
  462.— 
  Sieberella 
  Sieberi, 
  von 
  Buch. 
  Transverse 
  section, 
  showing 
  the 
  form 
  of 
  the 
  

   spondylia. 
  

  

  This 
  is, 
  however, 
  a 
  variable 
  feature, 
  the 
  septa 
  not 
  infrequently 
  

   forming 
  a 
  spondylium 
  supported 
  by 
  a 
  median 
  septum. 
  

   Type, 
  Sieberella 
  Sieberi, 
  von 
  Buch 
  (sp.). 
  

   Distribution. 
  Upper 
  Silurian 
  — 
  Lower 
  Devonian. 
  

  

  Gypidula, 
  Hall. 
  1867. 
  

   (Plate 
  48, 
  figs. 
  22-28.) 
  

  

  Shells 
  with 
  the 
  contour 
  of 
  Sieberella, 
  plicate 
  or 
  smooth. 
  

   Pedicle-valve 
  with 
  a 
  well-defined, 
  true, 
  cross-striated 
  cardinal 
  

   a,rea, 
  and 
  narrow, 
  but 
  erect 
  or 
  convex, 
  in- 
  

   cipient 
  deltidial 
  plates. 
  On 
  the 
  interior 
  the 
  

   teeth 
  are 
  unusually 
  strong, 
  the 
  septum 
  very 
  

   short, 
  the 
  spondylium 
  being 
  free 
  for 
  most 
  of 
  

   its 
  length. 
  In 
  the 
  opposite 
  valve 
  the 
  dental 
  

  

  r 
  Fig. 
  461. 
  — 
  Gypidula 
  sockets 
  are 
  distinct, 
  the 
  Crur.al 
  plates 
  ex- 
  

   transverse 
  section 
  in 
  panded 
  nearly 
  horizontally, 
  being 
  divided 
  at 
  

   front 
  of 
  the 
  short 
  median 
  their 
  beginning 
  by 
  a 
  narrow 
  median 
  cardinal 
  

  

  septum 
  of 
  the 
  pedicle- 
  mi 
  • 
  e 
  

  

  vaive; 
  showing 
  the 
  form 
  process. 
  The 
  inner 
  moiety 
  or 
  the 
  crural 
  plates 
  

   of 
  the 
  spondyiia 
  ig 
  Reflected 
  to 
  a 
  vertical 
  or 
  slightly 
  divergent 
  

  

  position 
  and 
  in 
  this 
  form 
  they 
  are 
  produced 
  anteriorly. 
  These 
  

   plates 
  rest 
  upon 
  two 
  broadly 
  convergent 
  septa 
  which 
  unite 
  with 
  

   the 
  valve 
  making 
  a 
  sessile 
  spondylium, 
  which 
  is 
  acute 
  at 
  its 
  

   anterior 
  extremity, 
  and 
  lies 
  at, 
  or 
  in 
  front 
  of 
  the 
  center 
  of 
  the 
  

  

  98 
  

  

  