﻿Report 
  of 
  the 
  State 
  Geologist. 
  1047 
  

  

  Shell-substance 
  finely|punctate. 
  

  

  Surface 
  smoother 
  covered 
  with 
  fine 
  concentric 
  striae, 
  accom- 
  

   panied 
  by 
  stronger 
  J 
  wrinkles 
  of 
  growth. 
  The 
  inner 
  laminae 
  are 
  

   sometimes 
  marked 
  |by 
  obscure 
  radiating 
  striae 
  near 
  the 
  margins 
  

   of 
  the 
  valves. 
  

  

  Type, 
  Newberria 
  Johannis, 
  Hall. 
  

  

  Distribution. 
  Middle 
  Devonian. 
  

  

  Centronella, 
  Billings. 
  1859. 
  

   (Plate 
  52, 
  figs. 
  1-7.) 
  

  

  Shells 
  plano-convex 
  or 
  concavo-convex. 
  Pedicle-valve 
  with 
  

   acute 
  incurved 
  beak, 
  perforated 
  at 
  its 
  extremity, 
  the 
  foramen 
  

   being 
  continuous 
  with 
  a 
  partially 
  closed 
  delthyrium; 
  medially 
  

   ridged, 
  andj 
  with 
  abruptly 
  sloping 
  sides. 
  On 
  the 
  interior 
  the 
  

   teeth 
  are 
  large, 
  thick 
  at 
  their 
  extremities 
  and 
  adherent 
  to 
  the 
  

   jateral 
  walls 
  of 
  the 
  shell. 
  Between 
  them 
  is 
  a 
  deep 
  pedicle 
  cavity, 
  

   in 
  the 
  bottom 
  of 
  which 
  lie 
  the 
  elongate 
  scars 
  of 
  the 
  adductor 
  

   muscles, 
  and 
  about 
  their 
  anterior 
  portion 
  the 
  small, 
  flabellate 
  

   diductors. 
  

  

  The 
  brachial 
  valve 
  is 
  very 
  shallow, 
  rendered 
  concave 
  exteriorly 
  

   by 
  a 
  median 
  sinus 
  which 
  does 
  not 
  make 
  itself 
  apparent 
  on 
  the 
  

   interior. 
  Beak 
  small, 
  apex 
  not 
  incurved. 
  Dental 
  

   sockets 
  broad, 
  bounded 
  interiorly 
  by 
  the 
  high 
  walls 
  

   of 
  the 
  hinge- 
  plate. 
  This 
  plate 
  is 
  divided 
  medially 
  

   by 
  a 
  deep 
  furrow 
  extending 
  to 
  the 
  apex, 
  and, 
  there- 
  

   fore, 
  consists 
  of 
  two 
  processes 
  which 
  are 
  elevated, 
  

   thickened 
  and 
  rest 
  on 
  the 
  bottom 
  of 
  the 
  valve. 
  

   From 
  the 
  anterior 
  face 
  of 
  these 
  arise 
  the 
  crura 
  troneiia 
  gians- 
  

   which 
  converge 
  for 
  a 
  short 
  distance, 
  and 
  expand 
  to 
  preparation 
  

   form 
  two 
  broad, 
  acute 
  jugal 
  processes. 
  From 
  here 
  showing 
  the 
  

   the 
  lateral 
  branches 
  of 
  the 
  brachidium 
  curve 
  out- 
  (romLhsro 
  1111 
  " 
  

   ward, 
  gradually 
  turning 
  from 
  a 
  vertical 
  to 
  a 
  horizontal 
  position, 
  

   broaden 
  rapidly 
  and 
  unite 
  to 
  form 
  an 
  anterior 
  triangular 
  plate 
  

   which 
  bears 
  a 
  median 
  ridge, 
  where 
  the 
  two 
  lateral 
  branches 
  

   are 
  conjoined. 
  The 
  whole 
  of 
  the 
  anterior 
  portion 
  of 
  the 
  brach- 
  

   idium 
  is 
  inclined 
  gently 
  upward 
  toward 
  the 
  cavity 
  of 
  the 
  opposite 
  

   ralve. 
  

  

  105 
  

  

  