﻿Report 
  of 
  the 
  State 
  Geologist. 
  1021 
  

  

  in 
  such 
  a 
  manner 
  as 
  to 
  form 
  an 
  elongate 
  cavity, 
  which 
  does 
  not 
  

   extend 
  to 
  the 
  bottom 
  of 
  the 
  valve. 
  Each 
  brancn 
  of 
  the 
  septum 
  

   supports 
  one 
  of 
  the 
  lateral 
  divisions 
  of 
  the 
  hinge-plate, 
  to 
  which 
  

   are 
  attached 
  the 
  curved 
  crural 
  processes. 
  In 
  normal 
  conditions 
  

   of 
  development 
  the 
  median 
  interspace 
  of 
  the 
  hinge-plate 
  is 
  not 
  

   closed. 
  The 
  dental 
  sockets 
  bordering 
  the 
  hinge-plate 
  are 
  crenu- 
  

   lated 
  in 
  the 
  typical 
  species. 
  There 
  is 
  no 
  cardinal 
  process. 
  

  

  In 
  the 
  pedicle-valve 
  slender 
  vertical 
  lamellae 
  support 
  the 
  

   rather 
  small 
  teeth 
  and 
  extend 
  well 
  into 
  the 
  cavity 
  of 
  the 
  valve, 
  

   inclosing 
  a 
  deep 
  and 
  narrow 
  pedicle-scar. 
  

  

  Type, 
  Camarotcechia 
  congregate 
  Conrad 
  (sp.). 
  

  

  Distribution. 
  Lower 
  Silurian 
  — 
  Lower 
  Carboniferous. 
  

  

  Subgenus 
  Plethorhynchus, 
  Hall. 
  1893. 
  

   (Plate 
  43, 
  figs. 
  10-15.) 
  

  

  Large, 
  ponderous 
  and 
  ventricose 
  shells 
  in 
  which 
  the 
  lateral 
  

   parts 
  of 
  the 
  hinge-plate 
  become 
  united, 
  closing 
  the 
  triangular 
  

   septal 
  cavity 
  but 
  forming 
  no 
  cardinal 
  process. 
  Dental 
  lamellae 
  

   faint, 
  evident 
  only 
  in 
  young 
  shells 
  ; 
  teeth 
  large 
  and 
  stout, 
  rest- 
  

   ing 
  on 
  the 
  lateral 
  walls 
  of 
  the 
  valve. 
  

  

  (Type, 
  Plethorhynchus 
  speciosus, 
  Hall. 
  Oriskany 
  sandstone.) 
  

  

  Subgenus 
  Liorhynchus, 
  Hall. 
  1860. 
  

   (Plate 
  43, 
  figs. 
  16-24.) 
  

  

  Shells 
  having 
  the 
  plications 
  on 
  median 
  fold 
  and 
  sinus 
  highly 
  

   developed, 
  but 
  those 
  on 
  the 
  lateral 
  slopes 
  usually 
  faint 
  or 
  

   obsolete. 
  Internal 
  structure 
  as 
  in 
  Camarotcechia 
  ; 
  adductor 
  scars 
  

   on 
  the 
  brachial 
  valve 
  forming 
  a 
  narrow, 
  elongate-oval 
  impression 
  

   divided 
  by 
  the 
  median 
  septum. 
  

  

  (Type, 
  Liorhynchus 
  quadricostatus, 
  Vanuxem 
  (sp.). 
  Devonian 
  — 
  

   Carboniferous.) 
  

  

  Wilsonia 
  (Quenstedt), 
  Kayser. 
  1871. 
  

   (Plate 
  44, 
  figs. 
  1-5.) 
  

   Shells 
  with 
  subcuboidal 
  or 
  subpentahedral 
  contour, 
  fold 
  and 
  

   sinus 
  not 
  sharply 
  developed 
  except 
  at 
  the 
  anterior 
  margin, 
  

   abrupt 
  anterior 
  slope, 
  sharply 
  serrated 
  lateral 
  margins 
  of 
  con- 
  

   tact 
  and 
  low 
  surface 
  plications, 
  each 
  of 
  which, 
  on 
  the 
  front 
  of 
  

   both 
  valves, 
  is 
  marked 
  by 
  a 
  fine 
  median 
  line. 
  Dental 
  plates 
  

  

  79 
  

  

  