﻿Report 
  of 
  the 
  State 
  Geologist. 
  1059 
  

  

  entire 
  structure 
  does 
  not 
  extend 
  beyond 
  the 
  middle 
  of 
  the 
  shell. 
  

   The 
  ascending 
  lamellae 
  are 
  very 
  fragile 
  and 
  usually 
  destroyed 
  in 
  

   fossilization. 
  

  

  Type, 
  Dielasma 
  elongatum, 
  Schlotheim 
  (sp.). 
  

  

  Distribution. 
  Devonian 
  (?) 
  — 
  Permian. 
  

  

  Subgenus 
  Cransena, 
  Hall. 
  1893. 
  

   (Plate 
  53, 
  figs. 
  4-9.) 
  

  

  Biconvex 
  shells 
  having 
  the 
  hinge-plate 
  constructed 
  as 
  in 
  

   Cryptonella 
  and 
  not 
  adherent 
  to 
  the 
  bottom 
  of 
  the 
  valve 
  as 
  in 
  

   Dielasma; 
  the 
  crura 
  also 
  arise 
  normally 
  from 
  

   the 
  lateral 
  divisions 
  of 
  this 
  plate. 
  Form 
  of 
  the 
  

   brachidium 
  as 
  in 
  Dielasma, 
  its 
  descending 
  

   branches 
  being 
  highly 
  divergent, 
  the 
  ascend- 
  

   ing 
  branches 
  abruptly 
  recurved, 
  making 
  a 
  

   broad, 
  gentle 
  curvature 
  above; 
  at 
  the 
  same 
  

   time 
  this 
  recurved 
  band 
  is 
  so 
  very 
  fragile 
  as 
  to 
  

   be 
  almost 
  invariably 
  destroyed. 
  The 
  entire 
  RomingeH, 
  Haiusp." 
  

   length 
  of 
  the 
  loop, 
  as 
  in 
  Dielasma, 
  and 
  in 
  An 
  outline 
  sh>wi 
  Dg 
  the 
  

  

  ° 
  , 
  . 
  . 
  r7 
  _. 
  7 
  Dielasma 
  frm 
  of 
  the 
  

  

  contradistinction 
  to 
  Cryptonella 
  and 
  Lunella, 
  brachidium 
  and 
  ihe 
  

   is 
  about 
  one-third 
  that 
  of 
  the 
  brachial 
  valve. 
  divided 
  hinge-piate. 
  

   (Type, 
  Crancena 
  Bomingeri, 
  Hall 
  (sp.). 
  Devonian.) 
  

  

  Dielasmina, 
  Waagen. 
  1882. 
  

  

  • 
  Plicated 
  shells 
  which 
  possess 
  more 
  or 
  less 
  of 
  the 
  characters 
  of 
  

   Dielasma. 
  They 
  have 
  the 
  dental 
  plates 
  of 
  the 
  pedicle-valve 
  and 
  

  

  Fig. 
  503. 
  Fig. 
  504. 
  

  

  Dielasmina 
  plicata, 
  Waagen, 
  

  

  Dorsal 
  and 
  front 
  views. 
  (Waagem.) 
  

  

  the 
  general 
  form 
  of 
  the 
  brachidium 
  in 
  that 
  genus, 
  as 
  far 
  as 
  

   the 
  interior 
  is 
  now 
  known. 
  

  

  Type, 
  Dielasmina 
  plicata 
  t 
  Waagen. 
  

  

  Distribution. 
  Carboniferous. 
  

  

  117 
  

  

  