﻿Report 
  of 
  the 
  State 
  Geologist. 
  

  

  1057 
  

  

  lamellae 
  are 
  fringed 
  with 
  rather 
  long, 
  irregularly 
  set 
  spinules 
  

   directed 
  toward 
  the 
  commissure 
  of 
  the 
  valves. 
  There 
  are 
  no 
  

   spinules 
  elsewhere 
  on 
  the 
  brachidium. 
  

  

  Centronella 
  (Harttina) 
  Anna, 
  Hartt. 
  

   Dorsal 
  and 
  profile 
  views 
  of 
  a 
  preparation 
  of 
  the 
  brachidium 
  ; 
  showing 
  the 
  hinge-plate, 
  broad 
  

   jugal 
  processes, 
  fimbriated 
  descending 
  lamellae, 
  lcng 
  recurved 
  lamellae, 
  and 
  prominent 
  median 
  

   septum 
  in 
  the 
  brachial 
  valve. 
  

  

  Type, 
  Harttina 
  Anna, 
  Hartt 
  (sp.). 
  

   Distribution. 
  Carboniferous. 
  

  

  Dielasma, 
  King. 
  1859. 
  

  

  (Plate 
  52, 
  figs. 
  10-25.) 
  

  

  Synonym; 
  Epithyris, 
  King 
  (not 
  Phillips), 
  1850. 
  

  

  Shells 
  biconvex; 
  outline 
  usually 
  el 
  on 
  gate- 
  oval; 
  frequently 
  a 
  

  

  median 
  sinus, 
  with 
  or 
  without 
  a 
  plication 
  at 
  the 
  bottom 
  of 
  it, 
  is 
  

  

  developed 
  in 
  both 
  valves. 
  

  

  The 
  apex 
  of 
  the 
  pedicle-valve 
  is 
  closely 
  incurved, 
  so 
  that 
  in 
  

   adult 
  shells 
  but 
  little 
  remains 
  of 
  the 
  deltidial 
  plates. 
  The 
  fora- 
  

   men 
  is 
  large, 
  quite 
  generally 
  encroaching 
  upon 
  the 
  umbo 
  and 
  

   often 
  becoming 
  very 
  oblique 
  to 
  the 
  longitudinal 
  axis 
  ; 
  with 
  the 
  

   increase 
  of 
  this 
  obliquity 
  the 
  deltidial 
  plates 
  are 
  thickened 
  on 
  

   their 
  inner 
  surface, 
  which 
  thus 
  becomes 
  more 
  or 
  less 
  protruded. 
  

   The 
  inverted 
  sheath 
  or 
  collar 
  within 
  the 
  foramen 
  is 
  highly 
  devel- 
  

   oped 
  and 
  clearly 
  shown 
  on 
  internal 
  casts. 
  On 
  the 
  interior 
  the 
  

   dental 
  plates 
  are 
  conspicuous, 
  and 
  stand 
  vertically 
  upon 
  the 
  

   bottom 
  of 
  the 
  valve, 
  not 
  showing 
  the 
  convergence 
  and 
  often 
  

   actual 
  union 
  occurring 
  in 
  Ceyptonella. 
  

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