﻿1044 
  FORTY-SEVEJSTH 
  REPORT 
  ON 
  THE 
  STATE 
  MUSEUM. 
  

  

  jugal 
  processes, 
  which 
  are 
  long, 
  pointing 
  upward 
  and 
  inward 
  but 
  

   not 
  uniting. 
  From 
  the 
  lower 
  angles 
  the 
  descending 
  arms 
  take 
  

   their 
  origin, 
  following 
  the 
  curves 
  of 
  the 
  valve, 
  diverging 
  for 
  a 
  

   short 
  distance, 
  thence 
  abruptly 
  approaching, 
  and 
  uniting 
  to 
  form 
  

   a 
  broad, 
  elongate, 
  acutely 
  triangular 
  plate, 
  which 
  is 
  not 
  sup- 
  

   ported 
  by 
  a 
  median 
  septum, 
  or 
  otherwise 
  connected 
  with 
  the 
  

   valve. 
  From 
  the 
  center 
  of 
  the 
  posterior 
  margin 
  of 
  the 
  plate 
  

   arises 
  a 
  small 
  rod-like 
  process, 
  which 
  extends 
  for 
  a 
  short 
  distance 
  

   upward 
  toward 
  the 
  crura. 
  

  

  The 
  muscular 
  area 
  is 
  less 
  clearly 
  delimited 
  than 
  that 
  of 
  the 
  

   opposite 
  valve, 
  and 
  its 
  component 
  scars 
  are 
  not 
  often 
  distinctly 
  

   defined. 
  It 
  is, 
  however, 
  broader 
  and 
  longer 
  than 
  on 
  the 
  pedicle- 
  

   valve, 
  and 
  is 
  divided 
  transversely 
  into 
  anterior 
  and 
  posterior 
  

   adductor 
  scars, 
  the 
  former 
  being 
  the 
  larger, 
  and 
  their 
  surface 
  

   covered 
  by 
  branching 
  lines 
  radiating 
  from 
  a 
  median 
  longitudinal 
  

   ridge. 
  From 
  the 
  narrow 
  and 
  somewhat 
  elevated 
  posterior 
  extrem- 
  

   ities 
  of 
  this 
  area 
  extends 
  a 
  broad 
  median 
  sinus, 
  on 
  either 
  side 
  of 
  

   which 
  arises 
  a 
  stout 
  vascular 
  trunk 
  bending 
  backward 
  and 
  over 
  

   the 
  post-lateral 
  slopes. 
  Secondary 
  branches 
  are 
  given 
  off 
  from 
  

   both 
  its 
  margins. 
  These 
  vascular 
  markings 
  of 
  the 
  genital 
  region 
  

   are 
  rarely 
  well 
  defined. 
  

  

  Surface 
  of 
  the 
  shell 
  distinctly 
  plicated, 
  with 
  sparse 
  concentric 
  

   wrinkles 
  near 
  the 
  anterior 
  margin. 
  The 
  radial 
  lines 
  may 
  be 
  fine 
  

   or 
  coarse, 
  but 
  no 
  species 
  is 
  known 
  in 
  which 
  the 
  surface 
  is 
  entirely 
  

   smooth. 
  

  

  Shell-substance 
  punctated 
  beneath 
  the 
  epidermal 
  layer. 
  

  

  Type, 
  Rensselceria 
  ovoides, 
  Eaton 
  (sp.). 
  Oriskany 
  sandstone. 
  

  

  Distribution. 
  Lower 
  Devonian. 
  

  

  Subgenus 
  Beachia, 
  Hall. 
  1893. 
  

   (Plate 
  51, 
  figs. 
  1-7.) 
  

  

  Shells 
  lentiform 
  in 
  general 
  contour; 
  moderately 
  and 
  sub- 
  

   equally 
  convex; 
  both 
  valves 
  with 
  an 
  obscure 
  and 
  undefined 
  

   median 
  fold. 
  The 
  beak 
  of 
  the 
  pedicle-valve 
  is 
  prominent, 
  never 
  

   incurved 
  sufficiently 
  to 
  conceal 
  its 
  deltidial 
  plates 
  and 
  foramen. 
  

   The 
  cardinal 
  margin 
  beneath 
  the 
  beak 
  is 
  flattened 
  into 
  a 
  well- 
  

   defined 
  pseudo-area, 
  and 
  the 
  short 
  inflection 
  of 
  the 
  margin 
  

   beginning 
  here 
  is 
  continued 
  along 
  the 
  lateral 
  portion 
  of 
  the 
  

  

  102 
  

  

  