﻿Report 
  of 
  the 
  State 
  Geologist. 
  1061 
  

  

  (?) 
  Cryptacanthia, 
  White 
  and 
  St. 
  John. 
  1867. 
  

   Shells 
  small 
  plano-convex 
  or 
  naviculoid. 
  Loop 
  long 
  and 
  

   recurved 
  ; 
  jugal 
  processes 
  united 
  above. 
  (?) 
  Outer 
  margins 
  of 
  the 
  

   brachidium 
  covered 
  with 
  spines. 
  

  

  Fig. 
  508. 
  

  

  Cryptacanthia 
  compacta, 
  White 
  and 
  St. 
  John. 
  

   A. 
  copy 
  of 
  the 
  original 
  figure. 
  

  

  (White 
  and 
  St. 
  John.) 
  

  

  Type, 
  Cryptacanthia 
  compacta, 
  White 
  and 
  St. 
  John. 
  

   Distribution. 
  Carboniferous. 
  

  

  Stringocephalus, 
  Defrance. 
  182T. 
  

   {emend. 
  Sandberger. 
  1842.) 
  

  

  Shells 
  varying 
  in 
  outline 
  from 
  transverse 
  to 
  elongate-oval 
  ; 
  

   biconvex, 
  the 
  brachial 
  valve 
  being 
  somewhat 
  the 
  deeper 
  ; 
  the 
  

   greater 
  convexity 
  is 
  in 
  the 
  umbonal 
  region, 
  giving 
  to 
  the 
  brachial 
  

   valve 
  a 
  high-shouldered 
  appearance. 
  

  

  On 
  the 
  pedicle-valve 
  the 
  beak 
  is 
  somewhat 
  narrow, 
  its 
  apex 
  

   being 
  abruptly 
  attenuate, 
  acute 
  and 
  often 
  greatly 
  incurved. 
  From 
  

   beneath 
  the 
  beak 
  diverge 
  two 
  sharp 
  ridges 
  extending 
  to 
  the 
  

   extremities 
  of 
  the 
  hinge, 
  and 
  delimiting 
  the 
  broad 
  cardinal 
  exca- 
  

   vations 
  which 
  seem 
  to 
  constitute 
  a 
  true 
  cardinal 
  area. 
  The 
  del- 
  

   thyrium 
  is 
  broad 
  and 
  triangular 
  ; 
  in 
  young 
  shells 
  it 
  may 
  be 
  wholly 
  

   open 
  or 
  incompletely 
  closed 
  by 
  the 
  imperfectly 
  developed 
  deltidial 
  

   plates, 
  while 
  at 
  maturity 
  it 
  is 
  closed, 
  with 
  the 
  exception 
  of 
  a 
  cir- 
  

   cular 
  foramen, 
  and 
  in 
  old 
  shells 
  the 
  deltidial 
  plates 
  are 
  anchylosed, 
  

   forming 
  a 
  single 
  plate 
  which 
  becomes 
  incurved, 
  and 
  the 
  foramina! 
  

   passage 
  is 
  thus 
  obscured, 
  and 
  may 
  take 
  the 
  form 
  of 
  a 
  tube 
  or 
  

   sheath 
  prolonged 
  into 
  the 
  umbonal 
  cavity. 
  

  

  On 
  the 
  interior 
  the 
  teeth 
  are 
  short, 
  free 
  and 
  curved 
  upward 
  at 
  

   their 
  extremities. 
  In 
  the 
  middle 
  of 
  the 
  valve 
  is 
  a 
  vertical 
  longi- 
  

   tudinal 
  septum, 
  which 
  extends 
  from 
  the 
  beak 
  to 
  near 
  the 
  anterior 
  

   margin. 
  This 
  septum 
  is 
  short 
  and 
  thick 
  posteriorly, 
  but 
  becomes 
  

  

  119 
  

  

  