﻿1012 
  Forty- 
  seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  oped 
  adult 
  conditions 
  this 
  thickening 
  is 
  absent, 
  the 
  extremities 
  

   of 
  the 
  processes 
  are 
  in 
  close 
  apposition, 
  or 
  may 
  form 
  a 
  continu- 
  

   ous 
  lamella. 
  The 
  muscular 
  impressions 
  consist 
  of 
  four 
  large 
  

   adductor 
  scars 
  divided 
  by 
  a 
  low 
  median 
  ridge. 
  

  

  Ovarian 
  pittings 
  and 
  vascular 
  sinuses 
  occur 
  over 
  the 
  inner 
  

   surfaces 
  of 
  both 
  valves. 
  The 
  latter 
  consist 
  of 
  two 
  main 
  trunks, 
  

   sending 
  two 
  branches 
  posteriorly, 
  and 
  two 
  longer 
  converging 
  

   branches 
  anteriorly. 
  

  

  External 
  surface 
  covered 
  with 
  radial 
  plications 
  crossed 
  by 
  

   concentric 
  growth-lines; 
  at 
  the 
  crossing 
  of 
  the 
  two 
  series 
  of 
  

   lines 
  the 
  external 
  layers 
  of 
  the 
  shell 
  may 
  be 
  produced 
  into 
  

   broad 
  lamellar 
  expansions 
  or 
  hollow 
  spines. 
  

  

  Shell-substance 
  fibrous, 
  impunctate. 
  

  

  Type, 
  Atrypa 
  reticularis, 
  Linne 
  (sp.). 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Lower 
  Carboniferous. 
  

  

  Subgenus 
  Gruenewaldtia, 
  Tschernyschew. 
  1885. 
  

   (Plate 
  41, 
  figs. 
  21,22.) 
  

  

  Atrypoid 
  shells 
  having 
  the 
  relative 
  convexity 
  of 
  the 
  valves 
  in 
  

   A. 
  reticularis 
  reversed. 
  Spiral 
  cones 
  with 
  their 
  bases 
  lying 
  

   against 
  the 
  lateral 
  slopes 
  of 
  the 
  pedicle-valve, 
  the 
  outer 
  face 
  of 
  

   the 
  cones 
  being 
  thus 
  parallel 
  to, 
  and 
  just 
  within 
  the 
  surface 
  of 
  

  

  Fig. 
  400. 
  Fig. 
  401. 
  

  

  Spirals 
  of 
  Gruenewaldtia 
  latilinguts, 
  Schnur. 
  In 
  fig. 
  401, 
  the 
  pedicle-valve 
  is 
  the 
  lower 
  and 
  

   the 
  two 
  median 
  dots 
  represent 
  sections 
  of 
  the 
  primary 
  lamellae. 
  (Tschsrnyschkw 
  .) 
  

  

  the 
  brachial 
  valve. 
  It 
  is 
  such 
  a 
  modification 
  of 
  the 
  brachial 
  

   apparatus 
  as 
  must 
  necessarily 
  ensue 
  from 
  the 
  variation 
  in 
  the 
  

   contour 
  of 
  the 
  shell. 
  The 
  character 
  of 
  the 
  jugum 
  has 
  not 
  been 
  

   determined. 
  

  

  (Type, 
  Gruenewaldtia 
  latilinguis, 
  Schnur 
  (sp.). 
  Lower 
  and 
  

   Middle 
  Devonian.) 
  

  

  70 
  

  

  