﻿1020 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  substance 
  of 
  the 
  valve. 
  Deltarium 
  very 
  conspicuous, 
  convex, 
  

   the 
  component 
  plates, 
  in 
  their 
  later 
  development, 
  being 
  anchy- 
  

   losed 
  along 
  the 
  median 
  suture. 
  Dental 
  lamellae 
  vertical, 
  resting 
  

   on 
  the 
  bottom 
  of 
  the 
  valve 
  and 
  inclosing 
  a 
  deeply 
  impressed 
  

   muscular 
  scar; 
  diductor 
  scars 
  elongate-flabelliform, 
  divided 
  by 
  

   oblique 
  ridges 
  into 
  anterior 
  and 
  posterior 
  members; 
  adductor 
  

   impression 
  central, 
  elongate 
  and 
  very 
  small. 
  The 
  brachial 
  

   valve 
  bears 
  a 
  median 
  septum 
  which 
  extends 
  for 
  one-half 
  the 
  

   length 
  of 
  the 
  shell, 
  is 
  divided 
  toward 
  its 
  posterior 
  extremity, 
  

   each 
  branch 
  supporting 
  one 
  process 
  of 
  the 
  divided 
  hinge-plate. 
  

   The 
  crura 
  are 
  long, 
  slightly 
  curved 
  and 
  somewhat 
  expanded 
  at 
  

   their 
  tips; 
  between 
  these 
  there 
  is 
  a 
  small, 
  simple, 
  cardinal 
  

   process. 
  

  

  External 
  surface 
  covered 
  with 
  exceedingly 
  fine, 
  rounded, 
  fili- 
  

   form, 
  concentric 
  lines. 
  Shell-substance 
  fibrous, 
  impunctate. 
  

  

  Type, 
  Rhynchotreta 
  euneata, 
  Dalman 
  (sp.). 
  

  

  Distribution. 
  Lower 
  — 
  Upper 
  Silurian. 
  

  

  Stenoschisma, 
  Conrad. 
  1839. 
  

   (Plate 
  42, 
  figs. 
  22-24.) 
  

  

  Sub 
  trihedral, 
  coarsely 
  plicate 
  shells 
  ; 
  teeth 
  supported 
  by 
  parallel 
  

   vertical 
  lamellae 
  ; 
  median 
  septum 
  of 
  the 
  brachial 
  valve 
  obscure 
  or 
  

   absent 
  ; 
  median 
  subcardinal 
  cavity 
  such 
  as 
  is 
  found 
  in 
  Camaro- 
  

   toechia, 
  wanting,' 
  the 
  hinge-plate 
  being 
  divided 
  by 
  a 
  median 
  

   fissure 
  which 
  extends 
  to 
  the 
  bottom 
  of 
  the 
  shell 
  and 
  contains 
  a 
  

   slender 
  longitudinal 
  cardinal 
  process 
  ; 
  crura 
  long, 
  recurved 
  and 
  

   expanded 
  at 
  their 
  extremities 
  ; 
  surfaces 
  of 
  the 
  dental 
  sockets 
  not 
  

   crenulated. 
  

  

  Type, 
  Stenoschisma 
  formosa, 
  Hall 
  (sp.). 
  

  

  Distribution. 
  Lower 
  Helderberg. 
  

  

  Camarotcechia, 
  Hall. 
  1892. 
  

   (Plate 
  43, 
  figs. 
  1-9.) 
  

   Shells 
  somewhat 
  variable 
  in 
  exterior 
  though 
  usually 
  main- 
  

   taining 
  a 
  full 
  trihedral 
  contour 
  with 
  shallow 
  pedicle-, 
  and 
  convex 
  

   brachial 
  valves, 
  evincing 
  little, 
  if 
  any, 
  evidence 
  of 
  a 
  reversal 
  at 
  

   maturity 
  of 
  the 
  relative 
  convexity 
  of 
  early 
  growth, 
  a 
  feature 
  

   apparent 
  in 
  some 
  of 
  the 
  other 
  groups 
  of 
  the 
  rhynchonelloids. 
  

   The 
  median 
  septum 
  of 
  the 
  brachial 
  valve 
  is 
  divided. 
  posteriorly 
  

  

  78 
  

  

  